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Here's code samples for learning C# quickly.

  1. The obligatory example for any language,

     
    using System;
    public class HelloWorld
    {
        public static void Main(string[] args) {
    	Console.Write("Hello World!");
        }
    }
    
  2. Raw CSharp compiler

    You can compile c# using the command line version

     
    C:>csc HelloWorld.cs
    
    and then run the new program by entering
    HelloWorld
    

    You can get Nant, a build tool like the old 'make', from http://sourceforge.net/projects/nant.

  3. Reading Stuff
    1. Read an entire file into a string

      using System;
      namespace PlayingAround {
          class ReadAll {
              public static void Main(string[] args) {
                  string contents = System.IO.File.ReadAllText(@"C:\t1");
                  Console.Out.WriteLine("contents = " + contents);
              }
          }
      }
      
    2. Read all the lines from a file into an array

       
      using System;
      namespace PlayingAround {
          class ReadAll {
              public static void Main(string[] args) {
                  string[] lines = System.IO.File.ReadAllLines(@"C:\t1");
                  Console.Out.WriteLine("contents = " + lines.Length);
                  Console.In.ReadLine();
              }
          }
      }
      
    3. Read a file line by line with no error checking

      Useful if the file may be really large.

       
      StreamReader sr = new StreamReader("fileName.txt");
      string line;
      while((line= sr.ReadLine()) != null) {
      	Console.WriteLine("xml template:"+line);
      }
      
      if (sr != null)sr.Close();  //should be in a "finally" or "using" block
      
  4. Writing Stuff
    1. Easy writing all text to a file

      WriteAllText will create the file if it doesn't exist, otherwise overwrites it. It will also close the file.

       
      using System;
      namespace PlayingAround {
          class ReadAll {
              public static void Main(string[] args) {
                  string myText = "Line1" + Environment.NewLine + "Line2" + Environment.NewLine;
                  System.IO.File.WriteAllText(@"C:\t2", myText);
              }
          }
      }
      
    2. Write a line to a file using streams

       
      using System;
      using System.IO;
      
      public class WriteFileStuff {
      
      public static void Main() {
             FileStream fs = new FileStream("c:\\tmp\\WriteFileStuff.txt", FileMode.OpenOrCreate, FileAccess.Write);			
             StreamWriter sw = new StreamWriter(fs);
             try {
      		sw.WriteLine("Howdy World.");
      	} finally {
      		if(sw != null) { sw.Close(); }
      	}
      }
      }
      
      
    3. Access files with "using"

      "using" does an implicit call to Dispose() when the using block is complete. With files this will close the file. The following code shows that using does indeed close the file, otherwise 5000 open files would cause problems.

       
      using System;
      using System.IO;
      
      class Test {
          private static void Main() {
              for (int i = 0; i < 5000; i++) {
                  using (TextWriter w = File.CreateText("C:\\tmp\\test\\log" + i + ".txt")) {
                      string msg = DateTime.Now + ", " + i;
                      w.WriteLine(msg);
                      Console.Out.WriteLine(msg);
                  }
              }
              Console.In.ReadLine();
          }
      }
      
      
    4. "using" as "typedef" (a la "C")

      "C" allows you to alias one type as another with typedef. In C# you can do this with "using" (can we create another overload for "using" just to make it more confusing?) Everywhere the type "RowCollection" is used, C# will understand it to be of type "List<Node>"

      using RowCollection = List<Node>;
    5. Write a very simple XML fragment the hard way.

       
      static void writeTree(XmlNode xmlElement, int level) {
         String levelDepth = "";
         for(int i=0;i<level;i++) 
         {
            levelDepth += "   ";
         }
         Console.Write("\n{0}<{1}",levelDepth,xmlElement.Name);
         XmlAttributeCollection xmlAttributeCollection = xmlElement.Attributes;
         foreach(XmlAttribute x in xmlAttributeCollection) 
         {
            Console.Write(" {0}='{1}'",x.Name,x.Value);
         }
         Console.Write(">");
         XmlNodeList xmlNodeList = xmlElement.ChildNodes;
         ++level;
         foreach(XmlNode x in xmlNodeList) 
         {
            if(x.NodeType == XmlNodeType.Element) 
            {
               writeTree((XmlNode)x,  level);
            }
            else if(x.NodeType == XmlNodeType.Text) 
            {
               Console.Write("\n{0}   {1}",levelDepth,(x.Value).Trim());
            }
         }
         Console.Write("\n{0}</{1}>",levelDepth,xmlElement.Name);
      }
      
    6. Write a very simple XML fragment the easier way

       
      StringWriter stringWriter = new StringWriter();
      XmlTextWriter xmlTextWriter = new XmlTextWriter(stringWriter);
      xmlTextWriter.Formatting = Formatting.Indented;
      xmlDocument.WriteTo(xmlTextWriter); //xmlDocument can be replaced with an XmlNode
      xmlTextWriter.Flush();
      Console.Write(stringWriter.ToString());
      
    7. To write any object or some collections to xml

      Object must have a default constructor.

      public static string SerializeToXmlString(object objectToSerialize) {
          MemoryStream memoryStream = new MemoryStream();
          System.Xml.Serialization.XmlSerializer xmlSerializer = 
              new System.Xml.Serialization.XmlSerializer(objectToSerialize.GetType());
          xmlSerializer.Serialize(memoryStream, objectToSerialize);
          ASCIIEncoding ascii = new ASCIIEncoding();
          return ascii.GetString(memoryStream.ToArray());
      }
      
    8. And this should turn the xml back into an object

      public static object DeSerializeFromXmlString(System.Type typeToDeserialize, string xmlString) {
          byte[] bytes = System.Text.Encoding.UTF8.GetBytes(xmlString);
          MemoryStream memoryStream = new MemoryStream(bytes);
          System.Xml.Serialization.XmlSerializer xmlSerializer = 
              new System.Xml.Serialization.XmlSerializer(typeToDeserialize);
          return xmlSerializer.Deserialize(memoryStream);
      }
      
      

      Example

      [Test]
      public void GetBigList() {
          var textRepository = ObjectFactory.GetInstance<ITextRepository>();
          List<BrandAndCode> brandAndCodeList = textRepository.GetList(...);
          string xml = SerializeToXmlString(brandAndCodeList);
          Console.Out.WriteLine("xml = {0}", xml);
           var brandAndCodeList2 = DeSerializeFromXmlString(typeof (BrandAndCode[]), xml);
      }
      
    9. A brief word on Types

      A Type has "data members" and "function members", like "int" which contains a value and has methods like "ToString()".

      All values in C# are instances of a type.

      C# provides built-in, or predefined, types directly in the language which the compiler understands and sets aside key words for them. The value types are sbyte, short, int, long, byte, ushort, uint, ulong, float, double, decimal, bool and char. The predefined reference types are string and object. These types are aliased into types in the "System" namespace, like "int" being an alias for System.Int32.

      C# also provides built-in types in the System namespace like DateTime, although the compiler has no direct knowledge of them.

      All C# types are in one of the following categories:
      Value types (mostly built-in types like "int", "double" and custom "struct" and enum which have no methods just a value, although with auto-boxing and implied methods it looks they do. This are stored on the stack.)
      Reference types (any class, arrays, delegates; anything which is a pointer to a block of memory, these are stored on the heap.)
      Generic type parameters, Pointer types

      You create your own Types with classes.

    10. Write formated output:

       
      int k = 16;
      Console.WriteLine(" '{0,-8}'",k);     // produces:  '16      '
      Console.WriteLine(" '{0,8}'",k);      // produces:   '      16'
      Console.WriteLine(" '{0,8}'","Test"); // produces:  '    Test'
      Console.WriteLine(" '{0,-8}'","Test");// produces: 'Test    '
      Console.WriteLine(" '{0:X}'",k);      //(in HEX) produces: '10'
      Console.WriteLine(" '{0:X10}'",k);    //(in HEX) produces:'0000000010'
      Console.WriteLine( 1234567.ToString("#,##0")); // writes with commas:   1,234,567
      
      
    11. namespace

      A namespace may be aliased to reduce clutter

      using Monkeys = Animals.Mammals.Primates;
      class MyZoo { Monkeys.Howler; }
      
    12. Formatting decimals in strings using String.Format()

      More info at www.codeproject.com

       
      s.Append(String.Format("Completion Ratio: {0:##.#}%",100.0*completes/count));
      
      or use the ToString() method on the double object:
       
      s.Append(myDouble.ToString("###.###")
      
      or
       
      String.Format("{0,8:F3}",this.OnTrack)
      
    13. Format DateTime objects

       
      DateTime.Now.ToString("yyyyMMdd-HHmm"); // will produce '20060414-1529'
      
  5. Example of Constructors, static Constructor and Destructor:

    using System;
    class Test2
       {
          static int i;
          static Test2() { // a constructor for the entire class called 
                           //once before the first object created
                  i = 4;
             Console.Out.WriteLine("inside static construtor...");
          }
          public Test2() {
             Console.Out.WriteLine("inside regular construtor... i={0}",i);
          }
          ~Test2() { // destructor (hopefully) called for each object
           Console.Out.WriteLine("inside destructor");
          }
          
          static void Main(string[] args)
          {
             Console.Out.WriteLine("Test2");
             new Test2();
             new Test2();
          }
       }
    

    Produces:

    inside static construtor...
    Test2
    inside regular construtor... i=4
    inside regular construtor... i=4
    inside destructor
    inside destructor
    
  6. Virtual and Non-Virtual Functions

    Here we see a non-virtual method. The object in:

    using System;
    namespace Test2 {
    class Plane { public double TopSpeed() {return 300.0D; }}
    class Jet : Plane { public double TopSpeed() { return 900.0D;}}
    class Airport {
    static void Main(string[] args) {
       Plane plane = new Jet();
       Console.WriteLine("planes top speed: {0}",plane.TopSpeed()); //300
       Console.ReadLine();
    }
    }
    }
    

    The above code, oddly enough will print "300" for the planes speed, since TopSpeed() is not virtual. To fix the problem we need to declare the method virtual *and* that the subclass "override"s the method. If we don't set Jet's method to override, we still get "300")

    class Plane { public virtual double TopSpeed() { return 300.0D;}}
    class Jet : Plane { public override double TopSpeed() { return 900.0D;}}
    class Airport {
    static void Main(string[] args) {
       Plane plane = new Jet();
       Console.WriteLine("planes top speed: {0}",plane.TopSpeed()); //900
       Console.ReadLine();
    }
    
  7. Hidden Inherited Members

    In a subclass you can reuse a variable name, but the compiler will warn you that the subclassed member is "hiding" the parent's variable

    public class Elephant { public int Weight = 15000; }
    public class AsianElephant : Elephant { public int Weight = 13000; }
    void Main()
    {
    Console.WriteLine(new AsianElephant().Weight); //13000
    }
    

    If a new variable is really want you want, tell the compiler to stop whining about it by using the "new" modifier (not to be confused with the "new" operator).

    public class AsianElephant : Elephant { public new int Weight = 1300; }
    
  8. Example of overloading an operator. Note many operators MUST be overloaded as a pair, eg, > , <

       public class Plane {
          public virtual double TopSpeed() { return 300.0D;}
          public static bool operator>(Plane one, Plane two) {   
             return one.TopSpeed() > two.TopSpeed();
          }
          public static bool operator<(Plane one, Plane two) {   
             return one.TopSpeed() < two.TopSpeed();
          }
       }
       class Jet : Plane {
          public override double TopSpeed() { return 900.0D; }
          public override string ToString() { return "I'm a Jet"; }
       }
          class Airport {
          static void Main(string[] args) {
             Plane plane = new Jet();
             Console.WriteLine("plane's top speed: {0}",plane.TopSpeed());
             Jet jet = new Jet();
             Console.WriteLine("jet's top speed: {0}",jet.TopSpeed());
             Console.WriteLine("Plane > Jet = {0}", plane > jet);
             Console.ReadLine();
          }
       }
    
    
  9. Overloading Arguments

    Given an overloaded method, the decision on which method to call is usually made at compile time based on the declared type of the argument. Even though the "mammal" object is really a Tiger type, the compiler will call the Mammal overload - unless you cast it to a "dynamic" type, in which case it will call the method based on the real type of the object.

    using System;
    namespace ScratchPad
    {
    public class Linnaeus 
    {
        public class Mammal {}
        public class Tiger : Mammal{}
        public static void Zoo(Mammal mammal)
        {
            Console.Out.WriteLine("mammal");
        }
        public static void Zoo(Tiger tiger)
        {
            Console.Out.WriteLine("tiger");
        }
        public static void Main(string[] args)
        {
            Mammal mammal = new Tiger();
            Zoo(mammal); //writes mammal because variable is that type
            Zoo((dynamic) mammal); //writes tiger because the object is a Tiger
            Console.ReadKey();
        }
    }
    }
    
    
  10. Example of using Properties instead of accessor methods. Note the special use of the "value" variable in "set".

    public class Plane {
     protected double mySpeed = 300.0D;
     public double TopSpeed { 
                     get {return mySpeed;} 
                     set { mySpeed = value; } 
                             }
    }
    class Jet : Plane {
       public Jet() { TopSpeed = 900.0D; }
    }
       class Airport {
       static void Main(string[] args) {
          Plane plane = new Plane();
          Console.WriteLine("plane's top speed: {0}",plane.TopSpeed);
          Jet jet = new Jet();
          Console.WriteLine("jet's top speed: {0}",jet.TopSpeed);
          Console.ReadLine();
       }
    }
    
  11. Write the current time

    DateTime dt = DateTime.Now;
    Console.WriteLine("Current Time is {0} ",dt.ToString());
    

    To specify a format: dt.ToString("yyyy/MM/dd")

    The cultural-independent universal format: dt.ToString("u")
    which prints "yyyy'-'MM'-'dd HH':'mm':'ss'Z'"

  12. Write a few lines to a file

    using System.IO;
    ...
    try {
     StreamWriter streamWriter = new StreamWriter("tmp.txt");
    
     streamWriter.WriteLine("This is the first line.");
     streamWriter.WriteLine("This is the second line.");
    } finally {
     if(streamWriter != null) {
         streamWriter.Close();
         }
    }
    
    
  13. Interacting with web servers

    1. Download a webpage into a string

      The simpliest approach is using WebClient if you are using a recent version of .Net.

       string webPageText;
       using (WebClient client = new WebClient())
       {
          webPageText = client.DownloadString("http://www.fincher.org");
       }
      
    2. Download a web page into a string using older .Net versions
       
      public static string GetWebPageAsString(string url) {
          HttpWebRequest httpWebRequest =(HttpWebRequest)WebRequest.Create(url);
          // you may need these next two lines to prevent a .net bug
          // System.IO.IOException : Unable to read data from the transport connection: The connection was closed.
          // see http://support.microsoft.com/default.aspx?scid=kb;EN-US;915599
          httpWebRequest.KeepAlive = false; 
          httpWebRequest.ProtocolVersion = HttpVersion.Version10; 
                  
          HttpWebResponse httpWebResponse = (HttpWebResponse)httpWebRequest.GetResponse();
          Stream stream = httpWebResponse.GetResponseStream();
          StreamReader streamReader = new StreamReader(stream, Encoding.ASCII);
          return streamReader.ReadToEnd();
      }
      
    3. How to do a POST to a website and return the html

      const string url = "http://MyHost.com/MyApp/MyAction";
      string pageText;
      string myParameters = "name=Tesla&occupation=inventor&nationality=Serbian";
      using (WebClient client = new WebClient())
      {
          client.Headers[HttpRequestHeader.ContentType] = 
              "application/x-www-form-urlencoded"; 
          pageText = client.UploadString(url, myParameters);
      }
       Console.Out.WriteLine("pageText = {0}", pageText);
      
    4. Download response with errors

      How to get the content of the page even with errors like 500 or 404 is shown below:

       public static string GetWebPageAsString(string url)
      {
          HttpWebRequest httpWebRequest = (HttpWebRequest) WebRequest.Create(url);
          HttpWebResponse httpWebResponse = null;
          string xml = "";
          try
          {
              httpWebResponse = (HttpWebResponse) httpWebRequest.GetResponse();
          }
          catch (WebException exception)
          {
              if (exception.Status == WebExceptionStatus.ProtocolError)
              { //get the response object from the WebException
                  httpWebResponse = exception.Response as HttpWebResponse;
                  if (httpWebResponse == null){ return "<Error />";}
              }
          }
          Stream stream = httpWebResponse.GetResponseStream();
          StreamReader streamReader = new StreamReader(stream, Encoding.ASCII);
          xml = streamReader.ReadToEnd();
          //streamReader.Close();
          if (httpWebResponse.StatusCode != System.Net.HttpStatusCode.OK)
          {
              throw new Exception(xml);
          }
      
          return xml;
      }
      
  14. Use System.Web.HttpUtility.HtmlEncode() to encode strings for display in the browser. Converts "<" to &lt;, a good first step against hacking on your site.

     this.Response.Write("<br />xml returned: \"" + HttpUtility.HtmlEncode(xml)  + "\"");
  15. Calculate Elapsed Time

    (DateTime.UtcNow is faster than DateTime.Now since it doesn't have to do the wacky daily savings time calculations).
     DateTime startTime = DateTime.UtcNow;
     // do stuff
     TimeSpan elapsed = DateTime.UtcNow - startTime;
     Console.WriteLine("response time: {0}",elapsed.TotalSeconds);
    

    Or you can you the handy Stopwatch class from System.Diagnostics

    using System;
    using System.Threading;
    using System.Diagnostics;
    namespace PlayingAround {
        class MyStopwatch {
            private static void Main() {
                var stopwatch = Stopwatch.StartNew();
                Thread.Sleep(50); //do something interesting here...
                stopwatch.Stop();
                long elapsedTimeInMilliSeconds = stopwatch.ElapsedMilliseconds;
                Console.Out.WriteLine("elapsedTimeInMilliSeconds = {0}", elapsedTimeInMilliSeconds);
                Console.Out.Write("press return to exit."); Console.In.ReadLine();
            }
        }
    }
    
  16. Get today's date at midnight

       value = DateTime.Today.ToString();
    

    What's the units for the argument to Sleep? You can make it more implicit by using TimeSpan.From* format:

                Thread.Sleep(TimeSpan.FromMilliseconds(50));
    
  17. How to convert a string to an integer, a string to a double, a string to a date...

    using System;
    class Parse {
    /// <summary>
    /// Example of various Parse methods
    /// </summary>
    private static void Main() {
    
        //all the types in .Net have a Parse method
        int i = int.Parse("34");
        bool b = bool.Parse("true");
        double d = double.Parse("234.333");
        DateTime dateTime = DateTime.Parse("2008-03-02 12:20am");
        
        //TryParse will return false if the parsing fails
        int intvalue;
        bool ok = int.TryParse("42", out intvalue); //ok = True, intvalue = 42
        ok = int.TryParse("abc", out intvalue); //ok = False, intvalue = 0
        
        //ParseExtact takes a format
        DateTime dt = DateTime.ParseExact("02-03-2008", "dd-MM-yyyy",
            System.Globalization.CultureInfo.CurrentCulture); //dt = 3/2/2008 12:00:00 AM
    
        Console.Out.WriteLine("dt = " + dt);
        Console.In.ReadLine();
    }
    }
    
  18. How to convert a double to an integer

    System.Convert contains many nifty little conversion routines.

    Convert.ToInt32(mydouble);
    
  19. Tiny Browser

    Source Code.

  20. Read a string from the console

    using System;
    class ReadLine
    {
        public static void Main()
        {
        Console.Write("Please enter your favorite animal: ");
        string animal = Console.ReadLine();
        Console.WriteLine("Good choice: " + animal);
        }
    }
    
    
  21. Xml and Xslt
    1. Read an xml file into a string

      using System;
      using System.IO;
      using System.Xml;
      
      class WriteXMLToString
      {
          //read an xml file and then write to a string 
          //(no error checking)
          public static void Main(string[] args)
          {
          XmlDocument xmlDocument = new XmlDocument();
          xmlDocument.Load(args[0]);
          StringWriter stringWriter = new StringWriter();
          XmlTextWriter xmlTextWriter = new XmlTextWriter(stringWriter);
          xmlTextWriter.Formatting = Formatting.Indented;
          xmlDocument.WriteTo(xmlTextWriter);
          xmlTextWriter.Flush();
          Console.Write(stringWriter.ToString());
          }
      }
      
      
      
    2. Read an xml file, twist it with an xsl file and then write to a string (no error checking)

      using System;
      using System.IO;
      using System.Xml;
      using System.Xml.Xsl;
      
      class WriteXMLViaXSL
      {
          //read an xml file, twist it with an xsl file and then write to a string (no error checking)
          public static void Main(string[] args)
          {
          XmlDocument xmlDocument = new XmlDocument();
          xmlDocument.Load(args[0]);
      
          XslTransform xslTransform = new XslTransform();
          xslTransform.Load(args[1]);
      
      
          StringWriter stringWriter = new StringWriter();
          XmlTextWriter xmlTextWriter = new XmlTextWriter(stringWriter);
          xmlTextWriter.Formatting = Formatting.Indented;
          xslTransform.Transform(xmlDocument, null, xmlTextWriter);
      
          xmlTextWriter.Flush();
          Console.Write(stringWriter.ToString());
          }
      }
      
    3. Another example reading xml and xslt info from two files and transforming with the more modern XslCompiledTransform

      [Test]
      public void Transform() {
          const string xmlFileNameWithPath = @"C:\workfiles\SwitchBoard\SwitchBoardHandler\Tests\Incidence1.xml";
          const string xslFileNameWithPath = @"C:\workfiles\SwitchBoard\SwitchBoardHandler\xslt\Incidence.xslt";
          XslCompiledTransform xslCompiledTransform = new XslCompiledTransform();
          xslCompiledTransform.Load(xslFileNameWithPath);
          StringBuilder stringBuilder = new StringBuilder();
          StringWriter stringWriter = new StringWriter(stringBuilder);
          xslCompiledTransform.Transform(xmlFileNameWithPath, null, stringWriter);
          stringWriter.Close();
          Console.Out.WriteLine("sb.ToString() = {0}", stringBuilder.ToString());
      }
      
    4. Transforming an xml string with an xslt file

       [Test]
      public void Transform() {
          const string xmlFileNameWithPath = @"C:\workfiles\SwitchBoard\SwitchBoardHandler\Tests\Incidence1.xml";
          const string xslFileNameWithPath = @"C:\workfiles\SwitchBoard\SwitchBoardHandler\xslt\Incidence.xslt";
          string xmlString = GetFileAsString(xmlFileNameWithPath);
          XmlTextReader xmlTextReader = new XmlTextReader(new StringReader(xmlString));
          XslCompiledTransform xslCompiledTransform = new XslCompiledTransform();
          xslCompiledTransform.Load(xslFileNameWithPath);
          StringBuilder stringBuilder = new StringBuilder();
          StringWriter stringWriter = new StringWriter(stringBuilder);
          xslCompiledTransform.Transform(xmlTextReader, null, stringWriter);
          stringWriter.Close();
          Console.Out.WriteLine("sb.ToString() = {0}", stringBuilder.ToString());
      }
      
    5. How to transform an xml string with an xsl string

      // <summary>
      /// transforms an xml string with an xsl string
      /// </summary>
      /// <param name="xmlString">xml to transform</param>
      /// <param name="XSLStylesheet">stylesheet</param>
      /// <returns>xml transformed</returns>
      public static string TransformXmlStringWithXslString(string xmlString, string XSLStylesheet)
      {
          //process our xml
          XmlTextReader xmlTextReader =
              new XmlTextReader(new StringReader(xmlString));
          XPathDocument xPathDocument = new XPathDocument(xmlTextReader);
      
          //process the xsl
          XmlTextReader xmlTextReaderXslt = new XmlTextReader(new StringReader(XSLStylesheet));
          XslCompiledTransform xslCompiledTransform = new XslCompiledTransform();
          xslCompiledTransform.Load(xmlTextReaderXslt);
      
          //handle the output stream
          StringBuilder stringBuilder = new StringBuilder();
          TextWriter textWriter = new StringWriter(stringBuilder);
          
          //do the transform
          xslCompiledTransform.Transform(xPathDocument, null, textWriter);
          return stringBuilder.ToString();
      }
      ...
      [Test]
      public void TransformXmlStringWithXsltString() {
          KoEndPoint koEndPoint = new KoEndPoint("test",null);
          string result = koEndPoint.TransformXmlStringWithXslString("<person name='Francis Bacon' />", "<xsl:stylesheet version='1.0' xmlns:xsl='http://www.w3.org/1999/XSL/Transform'><xsl:template match='/'>Person:<xsl:apply-templates select='*' /></xsl:template><xsl:template match='/person'><xsl:value-of select='@name' /></xsl:template></xsl:stylesheet>");
          Console.Out.WriteLine("result = " + result);
          result.ShouldEqual("<?xml version=\"1.0\" encoding=\"utf-16\"?>Person:Francis Bacon");
      }
      
      
    6. Creates an xml doc programatically and writes to the console and a file

      using System;
      using System.IO;
      using System.Xml;
      
      class CreateXMLDoc
      {
          //creates an xml doc programatically and writes to the console and a file
          public static void Main(string[] args)
          {
          XmlDocument xmlDocument = new XmlDocument();
              xmlDocument.PrependChild(xmlDocument.CreateXmlDeclaration("1.0", "", "yes"));
          XmlElement element = xmlDocument.CreateElement("Book");
          element.SetAttribute("author","Xenophone");
          element.AppendChild(xmlDocument.CreateTextNode("The Persian Expedition"));
          xmlDocument.AppendChild(element);
      
          StringWriter stringWriter = new StringWriter();
          XmlTextWriter xmlTextWriter = new XmlTextWriter(stringWriter);
          xmlTextWriter.Formatting = Formatting.Indented;
      
          xmlDocument.WriteTo(xmlTextWriter);
          xmlTextWriter.Flush();
          Console.Write(stringWriter.ToString());
              //get the value of the enviromental variable "TEMP"
          string filename = 
              System.Environment.GetEnvironmentVariable("TEMP")+"\\Book.xml";
          //write to a file in temp directory also
          xmlDocument.Save(filename);
          }
      }
      
    7. Convert XML to an HTML table

      C# has another set of libraries

      using System.Linq;
      using System.Text;
      using System.Xml.Linq;
      
      namespace SwitchBoard.Views.Handler {
          public class HandlerView {
              /// <summary>
              /// takes in well structured xml from something like 
              /// SELECT * FROM mytable AS XML AUTO
              /// where all the elements have identical attribues
              /// and creates an HTML table
              /// </summary>
              /// <param name="xml">collection of xml elements all with the same attributes</param>
              /// <returns>HTML table with class of 'xmlTable'</returns>
              public string ConvertXmlToHtmlTable(string xml) {
                  XDocument xDocument = XDocument.Parse("<outer>" + xml + "</outer>");
                  XElement root = xDocument.Root;
                  if(root == null || root.Elements().Count() == 0) return "Empty";
                  var xmlAttributeCollection = root.Elements().First().Attributes();
                  StringBuilder html = new StringBuilder("<table class='xmlTable'>\r\n<tr>");
                  foreach (var attribute in xmlAttributeCollection)
                  {
                      html.Append("<th>"+attribute.Name+"</th>");
                  }
                  html.Append("</tr>");
                  foreach (XElement element in root.Descendants())
                  {
                      html.Append("\r\n<tr>");
                      foreach (XAttribute attrib in element.Attributes()) {
                          html.Append("<td>"+attrib.Value+"</td>");
                      }
                      html.Append("</tr>");
                  }
                  html.Append("</table>");
                  return html.ToString();
              }
          }
      }
      
  22. To get a value from a form page

    private void Page_Load(object sender, System.EventArgs e) {
       string survey = Request.Params.Get("survey"));
       ...
    }
    
  23. To include the contents of a file inside an asp page

    <!--#include file="w:/mydir/data/Xsl/Footer.xsl" -->
    
    

    To read a file line by line.

    using System;
    using System.IO;
    
    public class Cat
    {
        public static void Main(string[] args) {
          string fileName = args[0];
          FileStream fileStream = null;
          try {
                fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read);
                StreamReader sReader = new StreamReader(fileStream);
                string line;
                while ((line = sReader.ReadLine()) != null) {
                	Console.WriteLine(line);
                }
          } catch(Exception e) {
              Console.WriteLine(e);
          } finally {
             if(fileStream != null) {
                 fileStream.Close();
             }
          }
        }
    }
    
  24. Read the QueryString and print to web page

    using System.Collections;
    using System.Collections.Specialized;
    ...
     NameValueCollection collection = Request.QueryString; 
     String[] keyArray = collection.AllKeys; 
     Response.Write("Keys:");
     foreach (string key in keyArray) {
        Response.Write("
    " + key +": "); String[] valuesArray = collection.GetValues(key); foreach (string myvalue in valuesArray) { Response.Write("\""+myvalue + "\" "); } }
  25. Example of dumping collection objects to HTML

    public static string ToHTML(Hashtable hashtable) {
         string tmp = "";
         IDictionaryEnumerator myEnumerator = hashtable.GetEnumerator();
         while ( myEnumerator.MoveNext() ) {
            tmp += "<br />" + myEnumerator.Key+", "+ myEnumerator.Value;
         }
         return tmp;
      }
    public static string ToHTML(ArrayList arrayList) {
       StringBuilder tmp = new StringBuilder(); //needs System.Text;
       foreach ( Object o in arrayList ) {
          tmp.Append("<br />" + o);
       }
       return tmp.ToString();
    }
    
  26. How to pass a variable number of arguments to a method using the ''params' method parameter modifier

    'params' must be the last parameter in the list.

    using System;
    
    public class Params {
    
    static private void Test(string name, params int[] list) {
       Console.Write("\n"+name);
       foreach(int i in list) {
          Console.Write(i);
       }
    }
    
    public static void Main(string[] args) {
       Test("test",1,2,3);
       Test("retest",1,2,3,4,5);
    }
    
    }
    

    The result looks like this:

     test123
     retest12345
    
  27. Example of executing commands from a csharp program

     ///<summary>
     ///executes a system command from inside csharp
     ///</summary>
     ///<param name="cmd">a dos type command like "isql ..."</param>
    
     ///<param name ="millsecTimeOut">how long to wait on the command</param>
    
     public static int executeCommand(string cmd, int millsecTimeOut) {
        System.Diagnostics.ProcessStartInfo processStartInfo = 
           new System.Diagnostics.ProcessStartInfo("CMD.exe", "/C "+cmd);
        processStartInfo.CreateNoWindow = true;
        processStartInfo.UseShellExecute = false;
        System.Diagnostics.Process process = 
           System.Diagnostics.Process.Start(processStartInfo);
        process.WaitForExit(millsecTimeOut); //wait for 20 sec
        int exitCode = process.ExitCode;
        process.Close();
        return exitCode;
     }
    
  28. Get an XML document from a web service

    Example of retrieving an XML document from a web service and then applying an XSLT stylesheet on the server side.

        public class ScreenerQuestionsToAsk : System.Web.UI.Page
        {
          private void Page_Load(object sender, System.EventArgs e) {
             GetSurveyDescriptorXMLService service = new
                                               GetSurveyDescriptorXMLService();
             XmlDocument xmlDocument = service.GetAllSurveyDescriptorsAsXMLDoc();
    
             string output = Util.WriteXMLViaXSL(xmlDocument,
                    "w:/mydir/data/Xsl/ScreenerQuestionsToAsk.xsl");
             Response.Write(output);
          }
        }
    
    
  29. Write XMLNodeList to Console

          public static string ToHTML(XmlNodeList xmlNodeList) {
             StringWriter stringWriter = new StringWriter();
             XmlTextWriter xmlTextWriter = new XmlTextWriter(stringWriter);
             xmlTextWriter.Formatting = Formatting.Indented;
             foreach(XmlNode xmlNode in xmlNodeList) {
                xmlNode.WriteTo(xmlTextWriter);
             }
             return stringWriter.ToString();
          }
    
  30. Returning an attribute from an XmlDocument

             string total = xmlDocument.SelectSingleNode("Surveys/Survey[@name='Beer']/cellName[@name='MatureBlueCollarMen']").Attributes.GetNamedItem("total").Value; 
    
    
  31. Exit message

      Console.WriteLine("Initialization failed. sorry.\r\n");
      System.Threading.Thread.Sleep(5000);  //same as java's Sleep()
      Environment.Exit(1);  //same as java's System.Exit(0);
    
  32. Tokenize string

    code to tokenize string into ArrayList

       string[] tokens = surveyName.Split(new char[] {':'});
       foreach (string item in tokens) {
          arrayList.Add(item);
       }
    
  33. Using "Split"

    Example of the StringSplitOptions.RemoveEmptyEntries option. This will remove the blank entries from the array.

    using System;
    class Animals {
    private static void Main() {
            string[] animals = "monkey,kangaroo,,,wallaby,,devil,,".Split(",".ToCharArray(),StringSplitOptions.RemoveEmptyEntries);
            foreach (string animal in animals) {
                Console.Out.WriteLine("animal = " + animal);
            }
            Console.In.ReadLine();
        }
    }
    
  34. Adding elements to an ArrayList with AddRange

    Instead of repeatedly calling Add() to initialize an arrayList, AddRange() can be used with the default initializer for an array.

    ArrayList ab = new ArrayList();
    ab.Add("a"); //old fashioned way
    ab.Add("b");
    ArrayList abcd = new ArrayList();
    abcd.AddRange(new string[] {"a","b","c","d"}); // new hip method
    
  35. Arrays

    Arrays can be jagged like C or Java, or true MultiDimensional arrays

    int[] iArray = new int[150]; //simple 1D array
    
      int [][]myArray = new int[2][]; //jagged array
      myArray[0] = new int[3];
      myArray[1] = new int[9];
    
    //MultiDimensional array
      string[,] AgeArray2D = {{"age","Young","14","50"}, 
                              {"age","Old","51","100"}};
     
    

    Shorthand for creating single dimension arrays

     double[] readings = new double[]{1.0, 2.4, 0.5, 77.2};
    
  36. NUnit

    Creating a master "TestAll" file to run other NUnit tests

    using NUnit.Framework;
    ...
     public void TestAllTests() {
        Test.write("\r\nStarting "+Name+" ...\r\n");
        TestSuite testSuite = new TestSuite("All Tests");
        TestResult testResult = new TestResult();
        //run setup fixtures
        testSuite.RunTest(
          new MyApplication11.TestRebuildDatabase("TestRebuildDatabase"),testResult);
        testSuite.RunTest(
          new MyApplication11.TestPopulateDatabase("TestPopulateDatabase"),testResult);
        //run the tests
        testSuite.AddTestSuite(typeof(MyApplication11.Test));
        testSuite.AddTestSuite(typeof(MyApplication11.TestSimple));
        testSuite.Run(testResult);
    
        Test.writeLine("Completed "+Name+" at "+DateTime.Now+"\r\n");
      }
    
    
  37. Working with our friend the database
    1. Accessing a database

      Let's return a single string from a database

       static public string GetSqlAsString(string sqlText,
                             SqlParameter[] sqlParameters,
                             string databaseConnectionString) {
          string result = "";
          SqlDataReader reader;
          SqlConnection connection = new SqlConnection(databaseConnectionString);
          using (connection) {
              SqlCommand sqlcommand = connection.CreateCommand();
              sqlcommand.CommandText = sqlText;
              if (sqlParameters != null) {
                  sqlcommand.Parameters.AddRange(sqlParameters);
              }
              connection.Open();
              reader = sqlcommand.ExecuteReader();
              if (reader != null)
                  if (reader.Read()) {
                      result = reader.GetString(0);
                  }
          }
          return result;
      }
      
      
    2. Timeout expired exception

      If you get the following exception:

      System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)

      Your command may really taking too long in the database and has been killed. You can increase the default time of 30 seconds by using the "CommandTimeout" field on the "Command" object as shown below:

      using (connection) {
          SqlCommand sqlcommand = connection.CreateCommand();
          sqlcommand.CommandTimeout = 60; //default is 30 seconds
          sqlcommand.CommandText = sqlText;
          ... 
      

      Don't be misled by the database connection string option, "Connection Timeout", e.g., "Data Source=myMachine; Integrated Security=SSPI; database=Northwind;Connection Timeout=60". That timeout is for getting the connection, not for how long it queries the database.

    3. Register a delegate

      Example of adding an InforMessage handler to a connection object.

           public static void MessageEventHandler( object sender, SqlInfoMessageEventArgs e ) {
               foreach( SqlError error in e.Errors ) {
                  Console.WriteLine("problem with sql: "+error);
                  throw new Exception("problem with sql: "+error);
               }
            }
            public static int executeSQLUpdate(string database, string command) {
               SqlConnection connection = null;
               SqlCommand sqlcommand = null;
               int rows = -1;
               try {
                  connection = getConnection(database);
                  connection.InfoMessage += new SqlInfoMessageEventHandler( MessageEventHandler );
                  sqlcommand = connection.CreateCommand();
                  sqlcommand.CommandText = command;
                  connection.Open();
                  rows = sqlcommand.ExecuteNonQuery();
                } catch(Exception e) {
                  Console.Write("executeSQLUpdate: problem with command:"+command+"e="+e);
                  Console.Out.Flush();
                  throw new Exception("executeSQLUpdate: problem with command:"+command,e);
               } finally {
                  if(connection != null) { connection.Close(); }
               } 
               return rows;
            }
      
      
      
    4. ExecuteScalar

      Example of a utility function that uses ExecuteScalar, and a utility function to free resources (which is now obsolete - you should use the "using" construct).

      public static int getSQLAsInt(string database, string command) {
               int i = -1;
               SqlConnection connection = null;
               SqlCommand sqlcommand = null;
               try {
                  connection = UtilSql.getConnection(database);
                  sqlcommand = connection.CreateCommand();
                  sqlcommand.CommandText = command;
                  connection.Open();
                  i = (int)sqlcommand.ExecuteScalar();
               } catch (Exception e) {
                  throw new Exception(Util.formatExceptionError("getSQLAsInt",command,e));
               } finally {
                  UtilSql.free(null,connection);
               }
               return i;
            }
      
      public static void free(SqlDataReader reader, SqlConnection connection) {
               try {
                  if(reader != null) { reader.Close(); }
               } catch (Exception) {}
               try {
                  if(connection != null) { connection.Close(); }
               } catch () {} // we don't have to declare Exception
      
            }
      
    5. Example of Parameterized SQL

      To avoid SQL injection attacks you should always use parameters

      using System;
      using System.IO;
      using System.Collections.Generic;
      using System.Text;
      
      using System.Data.SqlClient;
      using System.Data;
      
      namespace SQLTest {
      class SqlParameterization {
      /// <summary>
      /// example of using parameterized sql to avoid SQL injection attacks
      
      /// </summary>
         static void Main() {
            Console.Out.WriteLine("Authors whose state is CA:");
            SqlConnection sqlConnection = null;
            string dbconn = "Application Name=SqlTest; Data Source=localhost; Trusted_Connection=yes;  database=pubs";
            try {
              sqlConnection = new SqlConnection(dbconn);
              sqlConnection.Open();
      
              SqlCommand cmd = new SqlCommand("SELECT au_lname FROM Authors WHERE state = @state", sqlConnection);
              cmd.CommandType = CommandType.Text;
              SqlParameter param = new SqlParameter("@state", SqlDbType.Char, 2);
              param.Direction = ParameterDirection.Input;
              param.Value = "CA";
              cmd.Parameters.Add(param);
              SqlDataReader reader = cmd.ExecuteReader();
              while (reader.Read()) {
                 Console.WriteLine(String.Format("{0}", reader[0]));
              }
            } finally {
              if (sqlConnection != null) { sqlConnection.Close(); }
            }
            Console.In.ReadLine();
         }
       }
      }
      
      
      

      These lines

                 SqlParameter param = new SqlParameter("@state", SqlDbType.Char, 2);
                 param.Direction = ParameterDirection.Input;
                 param.Value = "CA";
      

      can be shortened to

                 SqlParameter param = new SqlParameter("@state", "CA");
      

      Since the default direction is "Input". Performance implications of the shortcut method are not known.

    6. Using SqlDataAdapter with Parameters

      conn = ... //connection string
      
      strSql = ... //sql string with @ variables like SELECT * FROM Authors WHERE name = @name
      DataSet dataSet = new DataSet();
      SqlDataAdapter dataAdapter = new SqlDataAdapter(strSql, conn);
      dataAdapter.SelectCommand.Parameters.Add(new SqlParameter("name", "OHenry"));
      dataAdapter.Fill(dataSet, "dataTable1"); 
      
      
    7. Convert DataTable to an XML string

      var dataTable = ... your amazing method goes here ...;
      string result;
      using (StringWriter sw = new StringWriter())
      {
          dataTable.WriteXml(sw);
          result = sw.ToString();
      }
      Console.Out.WriteLine("result = {0}", result);}
      
  38. Array sorting
  39. Example of using "using" to avoid the finally block mess

    a "using" block will execute its contents and then immediately call "Dispose()" on the using object. For connections, this will close the connection.

    using System;
    using System.Data.SqlClient;
    
    class Test {
        private static readonly string connectionString = "Data Source=myMachine; Integrated Security=SSPI; database=Northwind";
        private static readonly string commandString = "SELECT count(*) FROM Customers";
    
        private static void Main() {
            using (SqlConnection sqlConnection = new SqlConnection(connectionString)) {
                using (SqlCommand sqlCommand = new SqlCommand(commandString, sqlConnection)) {
                    sqlConnection.Open();
                    int count = (int)sqlCommand.ExecuteScalar();
                    Console.Out.WriteLine("count of customers is " + count);
                }
            }
            Console.In.ReadLine();
        }
    }
    

    To sort an array use the static method on Array class. (I don't know why array.sort() does not exist as a method)

    String[] keyArray = nameValueCollection.AllKeys;
    Array.Sort(keyArray);
    
  40. Using XPath

    The tricky thing about getting the attribute value is using the function 'string()' inside your XPath expression. Otherwise it returns a nodeSetIterator that you have to process.

    using System.Xml;
    using System.Xml.XPath;
    ...
    XPathDocument xPathDocument = new XPathDocument(fileName);
    XPathNavigator xPathNavigator = xPathDocument.CreateNavigator();
    
    string text = (string) xPathNavigator.Evaluate("string(//Survey[@name='"+survey+"']/@URL)");
    
  41. using block

    C# provides a special way of disposing of objects after their use - it's the "using" block. The object of the "using" statement must implement the IDisposable interface which contains one member, Dispose(). As shown below, after the "using" block is executed, Dispose() is immediately called.

    using System;
    namespace Doodle {
        class DisposableExample : IDisposable {
            public void Dispose() {
                Console.Out.WriteLine("I'm being disposed!");
            }
            public static void Main() {
                DisposableExample de = new DisposableExample();
                using (de) {
                    Console.Out.WriteLine("Inside using.");
                } //the compiler puts:  if(de != null) { de.Dispose(); }
                Console.Out.WriteLine("after using.");
                Console.In.ReadLine();
            }
        }
    }
    

    Produces:

    Inside using.
    I'm being disposed!
    after using.
    
  42. Getting property values from "Web.config" while in standalone test mode

    /// <summary>
    /// gets a property value from the Web.config file
    /// The problem with just using System.Configuration.ConfigurationSettings.AppSettings
    /// is that is doesn't work in standalone mode for unit testing e.g., nunit.cs
    /// </summary>
    /// <param name="property">property key name</param>
    /// <returns></returns>
        public static string getProperty(string property) {
          string propValue = "";
          try {
            if(System.Configuration.ConfigurationSettings.AppSettings.Count == 0) { 
              // we are in standalone mode
              XmlNodeList xmlNodeList = null;
              if(appSettings == null) {
                XmlDocument xmlDocument = new XmlDocument();
                //TODO: use the system environment or config methods instead
                // of hardcoded path
                xmlDocument.Load("c:/Inetpub/wwwroot/MyApplication11/Web.config");
                xmlNodeList =
                xmlDocument.SelectNodes("/configuration/appSettings/add");
                if(verbose) {
                  Console.Write("xmlNodeList.Count = " + xmlNodeList.Count); 
                  Console.Out.Flush();
                }
                appSettings = new NameValueCollection();
            
                foreach(XmlNode xmlNode in xmlNodeList) {
                  appSettings.Add(
                    xmlNode.Attributes.GetNamedItem("key").Value,
                    xmlNode.Attributes.GetNamedItem("value").Value);
                }
              }
              propValue = appSettings[property];
            } else { //we are in web mode
              propValue = (string)System.Configuration.ConfigurationSettings.AppSettings[property];
            }
          } catch (Exception e) {
            throw new Exception(Util.formatExceptionError("getProperty","getProperty:"+property,e));
          }
          return propValue;
        }
    
    
    
  43. Use Reflection to print all the fields and their values in an object, kinda like "inspect" in Ruby.

    Often its convenient to print the state of an object. Instead of overriding the ToString() method and explicitly printing each field, you can let C# do the work for you with a little bit of Reflection. You could even add code to recursively print the state of the composition objects as well. This is left as an exercise for the student.

      public override string ToString() {
        StringBuilder sb = new StringBuilder();
        System.Type type = this.GetType();
        sb.Append("\r\nInformation for "+type.Name);
        sb.Append("\r\nFields:");
        System.Reflection.FieldInfo[] fi = type.GetFields();
        foreach(FieldInfo f in fi) {
          sb.Append("\r\n  "+f.ToString()+ " = \""+ f.GetValue(this)+"\"");
        }
        System.Reflection.PropertyInfo[] pi = type.GetProperties();
        sb.Append("\r\nProperties:");
        foreach(PropertyInfo p in pi) {
          sb.Append("\r\n  "+p.ToString()+ " = \""+ p.GetValue(this,null)+"\"");
        }
        return sb.ToString();
      }
    
  44. Call a parent's constructor

    To call the parent's constructor:

    public Group(string xmlstring) : base (xmlstring) {
    }
    
  45. Calling one constructor from another

     
    //this constructor takes a single xmlElement argument, converts it to a string,
    //and calls the constructor that takes a string
    public SurveyStatus(XmlElement xmlElement) : this(To.ToText(xmlElement)) {}
    public SurveyStatus(string xmltext)  {
    ...
    }
    
  46. Append a node from text into an existing DOM.

    To import a new node into a DOM, we use the handy 'ImportNode()' method to avoid the 'not in document context' error.

      using System.Xml;
      using System.Xml.XPath;
      ...
      //create initial DOM
      XmlDocument xmlDocument = new XmlDocument(); 
      xmlDocument.LoadXml("<TextDefinitions name='DataSource'></TextDefinitions>");
      ...
      //add new node from xml text
      XmlDocument newXmlDocument = new XmlDocument();
      newXmlDocument.LoadXml("<text lang='en-UK' name='exit'>Goodbye</text>");
      XmlNode newNode = xmlDocument.ImportNode(newXmlDocument.DocumentElement,true);
      xmlDocument.DocumentElement.AppendChild(newNode);
    
  47. Get a text value from a DOM using XPath.

    Example C# fragment:

     
      using System.Xml;
      using System.Xml.XPath;
      ...
      //create initial DOM
      XmlDocument xmlDocument = new XmlDocument();
        ///   <TextDefinitions>
        ///     <TextDefinition name="DefaultDemographicText">
        ///        <Text lang="en-UK">Thanks for taking our survey.</Text>
        ///        <Text lang="fr-FR">Merci pour prendre notre apercu.</Text>
    
        ///     </TextDefinition>
        ///     <TextDefinition name="ExitText">
        ///        <Text lang="en-UK">Goodbye</Text>
        ///        <Text lang="fr-FR">Au revoir </Text>
    
        ///     </TextDefinition>
        ///   </TextDefinitions>
      xmlDocument.LoadXml("<TextDefinitions>  <TextDefinition name='DefaultDemographicText'>      <Text lang='en-UK'>Thanks for taking our survey.</Text>       <Text lang='fr-FR'>Merci pour prendre notre apercu.</Text>   </TextDefinition>   <TextDefinition name='ExitText'>       <Text lang='en-UK'>Goodbye</Text>       <Text lang='fr-FR'>Au revoir </Text>   </TextDefinition></TextDefinitions>");
      XPathNavigator xPathNavigator = xmlDocument.CreateNavigator();
      ...
    
       private string GetTextFromDOM(string textName,string lang) {
             string query = "string(/TextDefinitions/TextDefinition[@name='"+textName+"']/Text[@lang = '"+lang+"'])";
             string text = (string) xPathNavigator.Evaluate(query);
             if(verbose) { Util.write("GetTextFromDOM(\""+textName+"\", \""+lang+"\"): \""+text+"\""); }
             return text;
          }
       }
    
  48. How to return a single node using XPath expressions with the XmlDocument

        public static Survey GetSurvey(string groupName, string surveyName) {
             XmlDocument xmlSurveys = new XmlDocument();
             xmlSurveys.Load(filename);
             XmlNode xmlNode = (XmlNode) xmlSurveys.SelectNodes("//Survey[@name='"+surveyName+"']").Item(0);
    ...
          }
     
    
  49. Sort an ArrayList of non-trivial objects

    The IComparable interface needs to be supported. Fortunately, its only one method, CompareTo(Object obj).

    public class MyObject : ParentObject, IComparable {
    ...
    
    public int CompareTo(Object obj ) {
        MyObject myObject = (MyObject) obj;
        //priority is a double, which complicates matters, otherwise
        //  return this.priority-myObject.priority works well
        if(this.priority > myObject.priority) {
           return 1;
        } else if(this.priority < myObject.priority) {
           return -1;
        } else {
           return 0;
        }
     }
    }
    
    
    
    Then you can sort an ArrayList with "myObjectArrayList.Sort();" and C sharp will use your "CompareTo" method
  50. Example of using Interfaces

    As the following code shows, interfaces can be extended and, unlike classes, multiple interfaces can be extended

    using System;
    //example of interfaces
    public class Animals
    {
    //simple interface
    interface IAnimal {
      void Breathes();
    }
    //interfaces can inherent from other interfaces
    interface IMammal : IAnimal {
      int HairLength();
    }
    //interfaces can implement other interfaces which implemented interfaces
    interface IMarsupial : IMammal {
      int PouchSize();
    }
    //interfaces can implement many other interfaces
    interface IGonerMammal : IMammal, IExtinct {
    }
    interface IExtinct {
      int HowLongExtinct();
    }
    //classes can implement multiple interfaces
    public class TasmanianTiger : IGonerMammal, IMarsupial {
    public int PouchSize() { return 2; }
    public int HowLongExtinct() { return 28; }
    public int HairLength() { return 4; }
    public void Breathes() { }
    }
    
        public static void Main(string[] args) {
    	Console.Write("The Tasmanian Tiger has been extinct for {0} years", new TasmanianTiger().HowLongExtinct());
        }
    }
    
    
  51. Randomize C# ArrayList

    Utility to pseudo-randomize elements of an ArrayList in linear time
     public static void RandomizeArrayList(ArrayList arrayList, Random random) {
        if(arrayList == null) { return; }
        int count = arrayList.Count;
        for(int i=0;i<count;i++) {
           Object tmp = arrayList[i];
           arrayList.RemoveAt(i);
           arrayList.Insert(random.Next(count), tmp);
        }
     }
    
  52. Print out objects in Assmebly

             Assembly assembly = Assembly.GetAssembly(this.GetType());
             Type[] types = assembly.GetTypes();
             foreach(Type type in types) {
                write("type="+type);
             }
    
  53. Sort an ArrayList with an internal class

    class MyClass() {
    ...
    
       public class comparer: IComparer {
             public comparer() {}
             public int Compare(object obj1, object obj2) {
                return obj1.GetType().ToString().CompareTo(obj2.GetType().ToString());
             }
          }
    ...
    ArrayList arrayList = ...
    arrayList.Sort(new comparer());
    ...
    
  54. Create an instance of an object given its type

     object[]  paramObject = new object[] {};
     object obj = Activator.CreateInstance(type, paramObject);
    

    or
    string className = "MyType";
    MyType myType = (MyType) Activator.CreateInstance(Type.GetType(className), new object[]{});
    
  55. Using attributes on classes

    Example of using an attribute to determine if the associated SQL code for this object should be autogenerated. The Attribute code:

    using System;
    using System.Text;
    
    namespace MyApplication.Attributes {
    	[AttributeUsage(AttributeTargets.Class, AllowMultiple=false)]
    	public sealed class GenerateSQL : Attribute {
    		public bool YesOrNo;
    		public GenerateSQL(bool YesOrNo) {
    			this.YesOrNo = YesOrNo;
    		}
    	}
    }
    

    The placing of the attribute in a class

    namespace MyApplication {
    	[GenerateSQL(false)]
    	public class KQLogic : SDObjectSAS {
    ...
    

    The retrieving of the attribute from classes.

    object[] attr = sdObjectDb.GetType().GetCustomAttributes(  Type.GetType("MyApplication.Attributes.GenerateSQL"),false);
    if(attr != null && attr.Length > 0) {
       MyApplication.Attributes.GenerateSQL gs = (MyApplication.Attributes.GenerateSQL)attr[0];
       if(gs.YesOrNo == false) { //class has attribute and its set to false
           ....
    
  56. A Brief Note on Type

    Each object has a pointer to its type. The "GetType()" method will return, at runtime, the Type object describing the object. The "typeof" operator will do the same but usually at compile time. "typeof(string)"

  57. Utility to write a string to a file, and append to file

         public static void WriteStringToFile(string fileName, string contents) {
             StreamWriter sWriter = null;
             try {
                FileStream fileStream = new FileStream(fileName, FileMode.Create, FileAccess.Write);
                sWriter = new StreamWriter(fileStream);
                sWriter.Write(contents);
             } finally {
                if(sWriter != null) {
                   sWriter.Close();
                }
             }
          }
          public static void AppendStringToFile(string fileName, string contents) {
             StreamWriter sWriter = null;
             try {
                FileStream fileStream = new FileStream(fileName, FileMode.Append, FileAccess.Write);
                sWriter = new StreamWriter(fileStream);
                sWriter.Write(contents);
             } finally {
                if(sWriter != null) {
                   sWriter.Close();
                }
             }
          }
    
    
    
  58. Defining a web service

    Defining a web service is very easy. Add a reference to "System.Web.Services" in Visual Studio, add the "using System.Web.Services;" line in your code, subclass from "System.Web.Services.WebService" and finally put the "[WebMethod]" attribute on your method.

    ...
    using System.Web.Services;
    ...
       public class QuotaProxy : System.Web.Services.WebService {
    ...
          [WebMethod]
          public ArrayList GetSurveyStatus(string group, string lang, NameValueCollection DemographicResponses) {
    ...
    }
    
  59. Web Services

    To create a WSDL file for a service, just append "?wsdl" to the service name inside IE

    http://localhost/MyProject/Service1.asmx?wsdl
    
  60. Wrapper class for a WSDL

    Use the Wsdl.exe to read the WSDL document and create a wrapper class

    c:> Wsdl.exe "http://localhost/MyProject/Service1.asmx?wsdl"
    
  61. Global.asax Hooks

    'Global Event Handlers' can be set in this file

    protected void Application_Start(Object sender, EventArgs e) {
    	LogFile.WriteLine(" ** myApp Application starting at "+DateTime.Now);
    }
    
  62. Looking at an Assembly

    Code to trip through an assembly and print all public instance methods

         public void Coverage() { 
             writeMethodStart("Coverage");
             Assembly assembly = Assembly.LoadFrom("MyApplication.dll");
    		  foreach(Module module in assembly.GetModules()) {
    			  write("loading module "+module);
    			  Type[] types = module.FindTypes(null,null);
    			  foreach(Type type in types) {
    				  write(" ** "+type);
    				  MemberInfo[] memberInfoArray = type.GetMethods(BindingFlags.Public|BindingFlags.Instance|BindingFlags.DeclaredOnly);
    				  foreach(MemberInfo memberInfo in memberInfoArray) {
    					  write("     "+memberInfo.Name+"()");
    				  }
    			  }
    		  }
    
  63. How to use Dev Studio Debugger with NUnit GUI tests

    From xprogramming.com: Mark your breakpoint in DevStudio and start the NUnit GUI. Inside DevStudio select "Debug/Process/nuit-gui.exe" then "Attach". A new window pops up, select "Common Language Runtime". Run the test inside the GUI and DevStudio will stop at the breakpoint (ok, well, it should stop there).

  64. Temporarily disabling an NUnit method

    /// <summary>
    /// test of remoting
    /// </summary>
    [Test]
    [Ignore("Service often is not started on remote machine")]
    public void GetProjectList() { 
    	writeMethodStart("GetProjectList");
    	QPManager manager = new QPManager();
    	string xml = manager.GetProjectList("Test1", "en-UK", "gender:male").ToXml();
            write("manager.GetProjectList:"+xml);
    	writeMethodEnd();
    }
    
  65. Testing for the throwing of an exception

    If this method throws an exception, it will pass the test. If it doesn't throw an exception, it will fail the test.

    [Test, ExpectedException(typeof(Exception))]
    public void Get() { 
    	writeMethodStart(MethodInfo.GetCurrentMethod().ToString());
    	DatabaseObject.Get("IDontExist");
    	writeMethodEnd();
    }
    

    In later versions of NUnit you can use this syntax which is better

     Assert.Throws<Exception>(() => new MyObject(badargument));
    
  66. Static Constructors

    This constructor is only called once before the first object of this type is called. (Is it guarenteed to be called if no objects of its kind are never created?) It can only reference static objects of course and it has no parameters.

    public class SDObjectRespondent : SDObject {
    	public static DatabaseProxy databaseProxy = null;
    	public SDObjectRespondent() {}
    	public SDObjectRespondent(string xmlstring) : base(xmlstring) {}
    	static SDObjectRespondent() { 
    		databaseProxy = new DatabaseProxy(Util.GetRequiredProperty("RespondentDatabase"));
    	}
    }
    
  67. How to convert a string to a byte array?

    Use the handy (if somewhat obscure) System.Text.Encoding.UTF8 class

    byte[] buffer3 =  System.Text.Encoding.UTF8.GetBytes(xmltext);
    
    

    Don't be tempted by the Dark Side to do the following:

    string xmltext = sb.ToString();
    len = xmltext.Length;
    buffer = new byte[len];
    buffer =  System.Text.Encoding.UTF8.GetBytes(xmltext);
    

    Since not all characters in strings map to a small friendly byte (remember our European friends?) the count of characters in strings does not equal the number of bytes.

  68. Printing the name of the currently executing method

    The following will print "Void ExistInDatabase()"

    public void ExistInDatabase() {
    System.Console.Write(System.Reflection.MethodInfo.GetCurrentMethod().ToString());
    }
    
  69. How to remove items in an ArrayList using Remove().

    It's a little trickier than just doing a foreach() loop because you will get a InvalidOperationException. Instead use a simple for loop with a decrementing counter and remove them off the end.

    public void Remove(ArrayList surveyNamesToRemove) {
    if(surveyNamesToRemove == null || surveyNamesToRemove.Count == 0) { return; }
    for(int i=(surveyStatuses.Count-1); i>=0; i--) {
    	if(surveyNamesToRemove.Contains(((SurveyStatus)surveyStatuses[i]).GetName())) {
    		surveyStatuses.RemoveAt(i);
    	}
    }
    }
    
  70. switch statement

    int respondentSource = 1;
    ...
    switch(respondentSource) {
    	case 1:
    		respondent = new DynamicRespondent(group,lang);
    		break;
    	case 2:
    		respondent = Respondent.Get(iteration+1);
    		break;
    	case 3:
                    string xmlString = "<Respondent userID='2' />";
    		respondent = new Respondent(xmlString);
    		break;
    	default:
    		throw new Exception("Invalid switch option \""+respondentSource+"\"");
    }
    ...
    
  71. Environment.StackTrace

    This method recursively dumps the information from an exception.

    /// <summary>
    /// Formats an exception to be human readable.  If the exception has
    /// an inner exception, it recurses and prints that too.
    /// The Environment.StackTrace is also printed, since the usual stacktrace is
    /// truncated at times.
    /// </summary>
    /// <param name="e">thrown exception</param>
    /// <returns>string containing human readable exception</returns>
    
    public static string FormatException(Exception e){
    	StringBuilder sb = new StringBuilder();
    	sb.Append("\r\n *************** Exception ***************");
    	sb.Append("\r\ne.Message:\""+e.Message+"\"");
    	sb.Append("\r\ne.StackTrace:\""+e.StackTrace+"\"");
    	sb.Append("\r\ne.Source:\""+e.Source+"\"");
    	sb.Append("\r\ne.TargetSite:\""+e.TargetSite+"\"");
    	sb.Append("\r\nEnvironment.StackTrace:\""+Environment.StackTrace+"\"");
    	//recurse into inner exceptions
    	if(e.InnerException != null) {
    		sb.Append("\r\n ***************   Inner   ***************");
    		sb.Append(FormatException(e.InnerException));
    	}
    	return sb.ToString();
    }
    
  72. Validate an xml file to a schema programatically

    See also O'Reilly's Indroduction to Schemas, Microsoft's Roadmap for XML Schemas in the .NET Framework and IBM's Basics of using XML Schema.

    /// <summary>
    
    /// validate an xml file to a schema
    /// </summary>
    /// <param name="xmlString">string representation of xml file</param>
    /// <param name="schemaString">string representation of schema</param>
    /// <returns>null if its happy, otherwise a string containing error messages</returns>
    
    public static string ValidateXML(string xmlString, string schemaString) {
    	XmlTextReader xmlTextReader = new XmlTextReader(new StringReader(xmlString));
    	XmlValidatingReader xmlValidatingReader = new XmlValidatingReader(xmlTextReader);
    	xmlValidatingReader.ValidationType = ValidationType.Schema;
    	XmlSchema xmlSchema = new XmlSchema();
    	xmlSchema = XmlSchema.Read(new StringReader(schemaString),null);
    	xmlValidatingReader.Schemas.Add(xmlSchema);
    	Validate validate = new Validate();
    	ValidationEventHandler validationEventHandler = new ValidationEventHandler(validate.Validator);
    	xmlValidatingReader.ValidationEventHandler += validationEventHandler;
    	while (xmlValidatingReader.Read());
    	return validate.errors;
    }
    /// <summary>
    /// tiny class so we can have a ValidationEventHandler and collect the errors
    /// </summary>
    private class Validate {
    	public string errors = null;
    	public  void Validator(object sender, ValidationEventArgs args) {
               errors += args.Message + "\r\n";
    	}
    }
    
  73. Interface definition for Properties

    Properties may appear in an interace as the following example demonstrates:

    /// <summary>
    /// the inventory count for this item
    /// </summary>
    
    int inventory { get; set; }
    
  74. Dynamically invoking Static Methods

    How to invoke a static method on a dynamic object. This invokes the static method "Get(string name)" on a "myType" class object and returns an instance of a MyObjectType.

    using System.Reflection;            
    ...
    string objectType = "myType";
    //create an instance object
    MyObjectType objectTypeInstance =  (MyObjectType)Activator.CreateInstance(Type.GetType(objectType), null);
    //invoke static method and return an object of MyObjectType
    MyObjectType myObjectType = 
    	(MyObjectType)objectTypeInstance.GetType().InvokeMember ("Get",BindingFlags.Default | BindingFlags.InvokeMethod,null,null,new object [] {name});
    
  75. Dynamically invoking Instance Methods

    This example shows invoking an instance method on the "this" object, although any other object would work as well as long as you get the methodInfo object from its class.

    MethodInfo methodInfo = this.GetType().GetMethod("MyMethod");
    if(methodInfo != null) {	//invoke if method is really there
    		methodInfo.Invoke(this,param);
    }			
    ...
    
  76. Case-Insensitive Hashtable

    These are very handy when case doesn't matter.

     Hashtable hashTable = System.Collections.Specialized.CollectionsUtil.CreateCaseInsensitiveHashtable();
    
  77. With C#2.0 you should really use a type-safe Dictionary collection instead of hashtable most of the time.

    Here is an example of using a Dictionary with a Guid key and a Survey object as a value.

    using System.Collections.Generic;
    ...
    private static Dictionary<Guid,Survey> surveyByIdDictionary = null;
    private static readonly object surveyByIdDictionaryLock = new object();
    /// <summary>
    /// return Survey object based on id.
    /// If the id requested does not exist, a null is returned.
    /// </summary>
    
    /// <param name="id">guid of the survey of interest.</param>
    /// <returns>survey or null</returns>
    public static Survey GetById(Guid id) {
       if (surveyByIdDictionary == null) {
           lock (surveyByIdDictionaryLock) {
                if (surveyByIdDictionary == null) {
                    surveyByIdDictionary = new Dictionary<Guid, Survey>();
                    foreach (string surveyName in Survey.Default.GetNames()) {
                        Survey survey = Survey.Get(surveyName);
                        Survey.surveyByIdDictionary.Add(survey.id, survey);
                    }
                }
            }
        }
        return surveyByIdDictionary.ContainsKey(id) ? surveyByIdDictionary[id] : null;
    }
            
    
  78. How to get the directory of an executing web app

    
    string baseDir = AppDomain.CurrentDomain.BaseDirectory.Replace("bin", "");
    
  79. Case insensitive string compares

    Can you image a more verbose way to do it?

    if(CaseInsensitiveComparer.Default.Compare(name1,name2) == 0) 
    

    Which is more preferable I think than

    if(name1.ToLower() == name2.ToLower()) 
    

    or you can use the string.Equals with an extra argument

    
     if ( ! string.Equals(name1,name1,StringComparison.CurrentCultureIgnoreCase))
    
  80. How to do case-insensitive substrings searchs

    0 <= mystring.IndexOf(mysubstring, StringComparison.InvariantCultureIgnoreCase)
    
  81. Using indexers

    You can override the "[]" operator to return whatever you wish

    /// <summary>
    /// indexer method to get SurveyStatus object by name
    /// </summary>
    
    public SurveyStatus this[ string surveyName] {
    	get {
    		foreach(SurveyStatus ss in surveyStatuses) {
    			if(CaseInsensitiveComparer.Default.Compare(surveyName, ss.GetName()) == 0) {
    				return ss;
    			}
    		}
    		return null;
    	}
    }
    
  82. IEnumerable Interface

    The IEnumerable interface (.Net 2.0) implements only one method, "GetEnumerator()". This is an easy way to iterate over collections using foreach. The yield statement returns control to the calling routine and then picks up exactly where it left off. This can be advantageous if creating the elements is expensive since you don't have to create them until called.

    using System;
    using System.Collections;
    class DaysOfWeek {
        public class Days : IEnumerable {
            readonly string[] days = { "Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};
            public IEnumerator GetEnumerator() {
                for(int i=0;i<days.Length;i++) {
                    yield return days[i];
                }
            }
        }
        static void Main() {
            foreach (string day in new Days()) {
                Console.Write(day + " ");
            }
            Console.In.Read();
        }
    }
    
  83. Database Profiling Tip

    If you include the 'Application Name' in the connection string, the SQL profiler can show that to you. This makes db tuning easier.

    <add key="DB1ConnectionString" 
    
    value="Application Name=myAppName; Data Source=venus1; Trusted_Connection=yes; database=employees" />
  84. Show all the methods on an object

    using System.Reflection;
    ...
    MyObject myObject;
    foreach(MethodInfo meth in myObject.GetType().GetMethods()) {
    	Console.WriteLine(meth.ToString());
    }
    
  85. Creating a DOM programmatically

    [Test]
    new public void GenerateVenues() { 
    	writeMethodStart(MethodInfo.GetCurrentMethod().ToString());
    	
    	XmlDocument xdoc = new XmlDocument();
    	XmlElement root = xdoc.CreateElement("Schedule");
    	xdoc.AppendChild(root);
    	XmlElement day = xdoc.CreateElement("Day");
    	XmlAttribute date = xdoc.CreateAttribute("date");
    	date.Value = "2004/01/01";
           
    	day.SetAttributeNode(date);
    		XmlAttribute num = xdoc.CreateAttribute("number");
    	num.Value = "5";
    	day.SetAttributeNode(num);
    		root.AppendChild(day);
    		
    	write(To.ToText(xdoc));
    	writeMethodEnd();
    
    }
    
    

    This produces:

    <Schedule>
      <Day date="2004/01/01" number="5" />
    </Schedule> 
    
  86. Delegates
    1. Simple Delegates

      Delegates are objects that know how to run a method. Delegates are a refinement of method pointers in C, but with safety built in. The delegate object is bound to an method that takes the exact number and type of variables are arguments and returns the correct type.

      using System;
      
      public class DelegateTest
      {
      
      public static void PrintHello(string name) {
         Console.Write("Hello {0}!",name);
      }
      //define the MyPrinter type
      public delegate void MyPrinter(string s);
      
      public static void Main(string[] args) {
         //create an instance of MyPrinter delegate type
         MyPrinter myPrinter = PrintHello; //shorthand for "new MyPrinter(PrintHello);"
         myPrinter("Bill"); //invoke the delegate, shorthand for "myPrinter.Invoke("Bill")"
      }
      }
      

      Note: When you use the function name without the parentheses, e.g. "PrintHello", you are referring to a "method group" since the method may be overloaded. C# will pick the correct overloaded method based on the signature.

      Delegates, like strings, are immutable. When using "+=", you are creating a new Delegate.

    2. Asynchronous Delegate calls

      using System;
      //example of using Asynchronous Delegate calls
      public class DelegateTest
      {
      private static void Tick(int count) {
         for(int i=0;i<count;i++) {
           System.Threading.Thread.Sleep(1000); 
           Console.Out.WriteLine(".");
           Console.Out.Flush();
         }
      }
      public static string PrintHello(string name) {
         Tick(5);
         Console.Write("Hello {0}!",name);
         Tick(5);
         return name;
      }
      //define the MyPrinter type
      public delegate string MyPrinter(string s);
      
      public static void Main(string[] args) {
         //create an instance of MyPrinter delegate type
         MyPrinter myPrinter = new MyPrinter(PrintHello);
         IAsyncResult result = myPrinter.BeginInvoke("Bill",null,null);
         myPrinter("Uma");
         string tmp = myPrinter.EndInvoke(result);
         Console.Write("End of Program.  Returned value was "+tmp);
      }
      
      }
      
      
    3. Asynchronous Delegate calls with callback

      
      using System;
      using System.Runtime.Remoting.Messaging;
      
      //example of using Asynchronous Delegate calls with callback
      public class DelegateTest
      {
      public static void MyCallback(IAsyncResult iaresult) {
         AsyncResult result = (AsyncResult)iaresult;
         MyPrinter myPrinter = (MyPrinter)result.AsyncDelegate;
         Console.WriteLine("End of Program.  Returned value was "+myPrinter.EndInvoke(iaresult));
      }
      
      private static void Tick(int count) {
         for(int i=0;i<count;i++) {
           System.Threading.Thread.Sleep(1000); 
           Console.Out.WriteLine(".");
           Console.Out.Flush();
         }
      }
      public static string PrintHello(string name) {
         Tick(5);
         Console.Write("Hello {0}!",name);
         Tick(5);
         return name;
      }
      //define the MyPrinter type
      public delegate string MyPrinter(string s);
      
      public static void Main(string[] args) {
         //create an instance of MyPrinter delegate type
         MyPrinter myPrinter = new MyPrinter(PrintHello);
         IAsyncResult result = myPrinter.BeginInvoke("Bill",new AsyncCallback(MyCallback),null);
         myPrinter("Uma");
         //string tmp = myPrinter.EndInvoke(result);
         //Console.Write("End of Program.  Returned value was "+tmp);
      }
      
      }
      
      
    4. Multicast Delegates

      All delegates have multcast capability - they can call more than one method. You can use the "+=" operator to add methods to call (and "-=" to subtract them). They will be invoked in sequence starting with the first one. If you have a return value, only the last method called will return a value.

      MyDelegate m = MyMethod1;
      m += MyMethod2;
      
    5. Action<> and Func<TResult> Predefined delegates

      In .Net 3.5 the Action and Func delegates were defined in the System namespace.

      These predefined delegates can make your code less verbose and decrease coupling.

      The goal is to prevent redefining delegates over and over. Anders, the designer of C#, could have created something like this:

      public delegate void TakesAnIntAndReturnsVoid(int i);
      public delegate int TakesAnIntAndReturnsInt(int i);
      public delegate void TakesADoubleAndReturnsVoid(double x);
      public delegate double TakesADoubleAndReturnsADouble(double x);
      ...
      

      Then with a few thousand of these defined, you wouldn't need to create a delegate, just use one from the framework.

      But fortunately though the magic of generics, we can specify the types in a generic delegate.

      We can rewrite our first TestDelegate class shown a few sections above using Action and reduce the code volume.

       public class ActionTest
       {
           public static void PrintHello(string name)
           {
               Console.Write("Hello {0}!", name);
           }
           public static void Main(string[] args)
           {
               Action<string> myPrinter = new Action<string>(PrintHello); 
               myPrinter("Bill"); 
               
               Console.ReadKey();
           }
       }
      
    6. What is an Action?

      Action is a delegate defined in the System namespace that returns void.

      ...

      This allows us a shorthand to define delegates with up to 16 variables being passed in. Your on your own if you need 17.

    7. What is an Func?

      Func is similar to Action, but it returns a value.

      ...

      public static string Foo(int i, double x) { return "yes"; }
      private Func<int, double, string> myFunc = Foo;
      //a human would understand the above a "myFunc" is a 
      //function that takes an int and a double and returns a string.
      
  87. Sorted keys from a hashtable

    /// <summary>
    /// returns the keys of a hashtable in sorted order
    /// </summary>
    /// <param name="hashtable">unsorted type</param>
    
    /// <returns>sorted keys</returns>
    public static ArrayList GetSortedKeys(Hashtable hashtable) {
    	ArrayList arrayList = new ArrayList(hashtable.Keys);
    	arrayList.Sort(); //why couldn't Sort() return 'this' pointer?
    	return arrayList;
    }
    		
    
  88. "checked" keyword

    Oddly enough, by default, C# does not throw an exception for numerical overflows or underflows. To have C# check, you must use the "check" keyword, or configure your project to check all arithmetic.

    using System;
    //Example of using the "checked" keyword to catch over/under flows
    public class CheckedExample
    {
        public static void Main(string[] args) {
            int big = int.MaxValue - 1;
            int tooBig = big + 2; //overflow, but no error generated
            Console.WriteLine("big = {0}",big); 
            Console.WriteLine("tooBig = {0}",tooBig);
    
            try { 
               checked {
                  tooBig = big + 2; //exception generated
               }
            } catch (OverflowException e) {
                Console.WriteLine(e.ToString());
            }
        }
    }
    
    

    The output is:

     big = 2147483646
     tooBig = -2147483648
     System.OverflowException: Arithmetic operation resulted in an overflow.
        at CheckedExample.Main(String[] args) in C:\home\mfincher\csharp\CheckedExample.cs:line 13
    
    

    To check for under/overflows for the entire program you can use a compiler switch, "/checked+". If you need to not check a particular expression, use "unchecked { ... }".

  89. Implicit and Explicit Type Conversions

    C# will automatically convert some types for us if the following two conditions are true:
    1. The compiler can know the conversion will succeed
    2. No information is lost during the conversion

    int big = 32768; //one bigger than a "short" can store
    short tiny = 1;
    tiny = (short)big;// the compiler knows we may lose information, but allows
                      // the conversion since it might work and it 
    		  // trusts us to do the right thing.
    		  // Although in our case it doesn't work.  We have failed the compiler.
    Console.Out.Write(tiny); //-32768
    
  90. Default values

    Variables not assigned a value are given default values; all reference types are set to null, numeric and enums are set to zero, char is set to '\0', and bool is set to false. If you need to get the default value, you can use the "default" keyword. You can even use it on generics: default(Cacher<string>)

    int a = default(int);
    Console.WriteLine(a);// 0
    
  91. Downcasting and Upcasting

    C# will automatically upcast a type for you (making a subclass a parent class), but you must explicitly do a downcast, since it might fail.

  92. class Mammal {}
    class Rabbit : Mammal{}
    void Main()
    {
    Rabbit rabbit = new Rabbit();
    Mammal mammal = rabbit; //upcast done automatically, can't fail
    
    Rabbit peter = (Rabbit)mammal; //must explicitly downcast, since it may fail
    }
    
    
  93. How to convert one type of object to another using a cast
    using System;
    //hokey example of using explicit conversion
    public class Conversion
    {
    public class Circle {
       public double x,y,r;
       public Circle(double x, double y, double r) {
          this.x = x; this.y = y; this.r = r;
       }
    }
    
    public class Square {
       public double x,y,width;
       public Square(double x, double y, double width) {
          this.x = x; this.y = y; this.width = width;
       }
       public override string ToString() {
        return String.Format("Square x={0} y={1} width={2}",x,y,width);
       }
       //show the object how to cast a circle to be a square
       public static explicit operator Square(Circle circle) {
           return new Square(circle.x,circle.y,circle.r);
       }
    }
    
        public static void Main(string[] args) {
            Circle c = new Circle(1.0,1.0,2.0);
            Square s = (Square)c;
    	Console.Write("Converted circle to square!  "+s.ToString());
        }
    }
    

    A tiny programming joke: (theWind) fate;

  94. How to return more than one object from a method call.

    Using the "out" or the "ref" parameter modifier will allow values to be returned.

     
    using System;
    //Example showing use of the out method parameter modifiers
    public class RefOut {
        public void test(out string text) {
    	text = "inside";
        }
        public static void Main(string[] args) {
    	RefOut refOut = new RefOut();
    	string text = "outside";
    	refOut.test(out text);
    	Console.WriteLine("text="+text); //text=inside
        }
    }
    

    "out" is often used to return more than one value from a method.

  95. public void calculateInterest(decimal loanAmount, out decimal interest, out decimal payment) {
    

    What's the difference between "ref" and "out"? "ref" requires that an object is assigned before passing it to the method. "out" requires the method being called to assign a value the the variable.

    Example of using "ref"

    using System;
    class RefMagic {
    
     private void Renamer(ref string name) {
         name = "Joe";
     }
        static void Main() {
            string name = "Mike";
            Console.Out.WriteLine("name = " + name);
            RefMagic refMagic = new RefMagic();
            refMagic.Renamer(ref name);
            Console.Out.WriteLine("name = " + name);
            Console.In.Read();
        }
    }
    

    Produces:

    
    name = Mike
    name = Joe
    
  96. How to pass a variable number of arguments to a method

    Use the "params" modifier, which must be modifying the last argument.

    using System;
    class MyDoodle {
        //example of passing a variable number of arguments to a method
        private static int Addem(params int[] myarray) {
            int sum = 0;
            foreach (int i in myarray) {
                sum = sum + i;
            }
            return sum;
        }
    
        static void Main() {
            Console.Out.WriteLine("sum = " + Addem());
            Console.Out.WriteLine("sum = " + Addem(1, 2));
            Console.Out.WriteLine("sum = " + Addem(1, 2, 3, 4, 5, 6));
            Console.In.Read();
        }
    }
    
  97. How to loop through a list of files in a directory

    This looks at all files ending in ".cs"

    using System;
    using System.IO;
    
    public class Temp
    {
        public static void Main(string[] args) {
        DirectoryInfo di = new DirectoryInfo(".");
    	foreach(FileInfo fi in di.GetFiles("*.cs")) {
    		Console.WriteLine("Looking at file \""+fi.FullName+"\"");
            }
       }
    }
    

    The results:

       Looking at file "C:\home\mfincher\csharp\Animals.cs"
       Looking at file "C:\home\mfincher\csharp\AsyncDelegateTest.cs"
       Looking at file "C:\home\mfincher\csharp\CheckedExample.cs"
       Looking at file "C:\home\mfincher\csharp\Conversion.cs"
    

    A caveat: DirectoryInfo.GetFiles will sometimes return more than you want. It will also return files whose extension has extra characters. Looking for "*.xml" will also yield "*.xmlabc" which can be, at the least, annoying.

    foreach (var fileInfo in dirInfo.GetFiles("*.xml"))
    {
        if(fileInfo.Extension != ".xml") continue; //gets rid of "SDUS.xml~"
        using (var reader = new XmlTextReader(fileInfo.FullName))
        ...
    }
    
  98. How to walk up a directory tree looking for a file

    For example, you may want to find a "config" directory which is a few levels above your executing directory. Use something like "Assmebly.GetAssembly" to find a startingDirectory and "\\Config\\settings.xml" for a target file.

     private static string WalkDirTreeUpwardsAndSearchForFile(string startingDirectory, string targetFilename) {
                string path = startingDirectory;
                string fullFilename = path + targetFilename;
                while (!File.Exists(fullFilename) && path != null) {
                    path = Path.GetDirectoryName(path);//walk up a directory
                    fullFilename = path + targetFilename;
                }
                if (!File.Exists(fullFilename)) {
                    throw new Exception(string.Format("Could not find file '{0}' starting in directory '{1}'", targetFilename, startingDirectory));
                }
                return fullFilename;
            }
    
  99. How to convert a relative path to an absolute path

    string directoryName = Path.GetFullPath(@"..\..\..\..\..\Data\xsd\Surveys.xsd");
    Console.Out.WriteLine("directoryName = {0}", directoryName); //C:\workfiles\SurveyDirector\src\Data\xsd\Surveys.xsd
    
  100. How to spawn a separate process and kill it.

    This launches an instance of the browser, waits 15 seconds and then closes it.

    using System;
    using System.IO;
    using System.Diagnostics;
    using System.Threading;
    
    public class Temp
    {
    	/// <summary>
    
    	/// Example of creating an external process and killing it
    	/// </summary>
    	public static void Main() {
        
        Process process = Process.Start("IExplore.exe","www.cnn.com");
        Thread.Sleep(15000);
        	try {
        		process.Kill();
        	} catch {}
       }
    }
    
  101. How to execute a background process repeatedly

    Using a Timer with a TimerCallback you can tell .Net to repeatedly invoke a method on a schedule. The code is a little verbose for instructional purposes.

    using System;
    using System.Threading;
    
    public class RegistrarProxy {
        private static Timer _timer;
        private static readonly TimerCallback _timerCallback = timerDelegate;
        
        public void Init() {
            _timer = new Timer(_timerCallback, null, 0, 2000); //repeat every 2000 milliseconds
        }
    
        private static void timerDelegate(object state) {
            Console.WriteLine("timerDeletegate: "+DateTime.Now);
        }
    
        public static void Main() {
            RegistrarProxy rp = new RegistrarProxy();
            rp.Init();
            Console.In.Read(); //let's wait until the "return" key pressed
        }
    }
    
  102. Example of Serialization using the Xml Formatter

    The binary and SOAP formatters are more useful in most situations.

    using System;
    using System.Xml;
    using System.Xml.Serialization;
    using System.IO;
    
    public class SerializeExample
    {
    	[Serializable]
    	public class Employee {
    		public string name;
    		public int yearOfBirth;
    		public Employee(string name, int yearOfBirth) {
    			this.name = name; this.yearOfBirth = yearOfBirth;
    		}
    		public Employee() {} //needed for serialization
    	}
        public static void Main(string[] args) {
    	Console.Write("starting serialization...");
        FileStream fileStream = File.Create("SerializeExample.xml");
        XmlSerializer xmlSerializer = 
                      new XmlSerializer(typeof(Employee),"Employee");
        xmlSerializer.Serialize(fileStream,new Employee("Achilles",1972));
        fileStream.Close();
        Console.Write("done.");
        }
    }
    
    

    Contents of the file:

    
    <?xml version="1.0"?>
    <Employee xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xmlns="Employee">
      <name>Achilles</name>
      <yearOfBirth>1972</yearOfBirth>
    </Employee>
    
  103. How to inject your company name etc. into the assembly

    By default dev studio creates a small file for you called "AssemblyInfo.cs". Inside are various assembly-level attributes. If you fill these in, then when the .dll is queried via a right mouse click and "Properties" selection, the information will appear in the dialog box.

    [assembly: AssemblyCompany("Acme Enterprises")]
    
  104. How to create an Enum value from the string representation

    public enum Action { run, walk, skip };
    
    string action = "Run";
    Action myaction = (Action)Enum.Parse(typeof(Action),action);
    
    if(myaction == Action.run) 
    ...
    
  105. Null Coalescing Operator, aka the double question mark operator

    The tertiary operator '?' has a friend, the '??' operator. If the value before the '??' is non-null, the value is returned. If the value is null, the value after the '??' is returned. The two statements below work identically.

           s = (name != null) ? name : "";
           s = name ?? ""; //returns "" if name is null, otherwise returns name
    
  106. ASP.NET Example code

    1. Validate a textbox widget
      Enter your name 
      <asp:TextBox Runat=server id=TextBox1 />
              <asp:RequiredFieldValidator ControlToValidate=TextBox1
              Runat="server">
              You must supply a name.
              </asp:RequiredFieldValidator>
      
    2. How to create a cookie in asp.net

      <%
          HttpCookie aCookie = new HttpCookie("MyCookieName");
          aCookie.Value = "MyCookieValue";
          aCookie.Expires = DateTime.Now.AddDays(100);
          Response.Cookies.Add(aCookie);
      %>                                                             
      
    3. Get the IP address of the browser

      On the aspx page:

      protected void Page_Load(object sender, EventArgs e) {
             string ip = Request.UserHostAddress;
             ...
      
    4. Show a result set in a broswer window.

      On the aspx page:

      <asp:GridView ID="GridViewResults" runat="server" />
      

      In the code behind:

      DataSet ds = databaseProxy.GetSqlAsDataSet("SELECT * FROM candidate_data ORDER BY dtime DESC","Poll");
      GridViewResults.DataSource = ds;
      GridViewResults.DataBind();
      
    5. Set an item in a dropdownlist as the currently selected

      System.Web.UI.WebControls.DropDownList StatusDropDownList;
      //...(add members)
      StatusDropDownList.Items[StatusDropDownList.SelectedIndex].Selected = 
          false;
      StatusDropDownList.Items.FindByValue(surveyDescriptor.Status).Selected = 
          true;
      
    6. To catch all the unhandled exceptions in a Page

      This will allow you to make sure all the errors encountered at the top level get logged.

      private void Page_Error(object sender, System.EventArgs e) {
      	Exception ep = Server.GetLastError();
      	LogFile.LogFatal(Util.FormatExceptionError("Page_Error","top level error", ep,4));
      	//Server.ClearError(); //we don't clear, but let the system produce message
      }
      
      

      To have the above run, it must be registered as a callback

      private void InitializeComponent() {    
      	this.Load += new System.EventHandler(this.Page_Load);
      	this.Error += new System.EventHandler(this.Page_Error);
      }
      		
      
    7. To store data in a respondent's session

      Session["favAnimal"] = "zebra";
      //and retrieve it later...
      string animal = (string) Session["favAnimal"];
      
    8. How an application can be notified of changes to a file

      You can set a FileWatcher to invoke a callback whenever a file is changed by an external force.

      using System;
      using System.IO;
      
      namespace DefaultNamespace
      {
      	/// <summary>
      
      	/// Description of Class1.	
      	/// </summary>
      	public class FileWatcher
      	{
      		public FileWatcher()
      		{
      		}
      		public static void Main() {
      			FileSystemWatcher fileSystemWatcher = new FileSystemWatcher();
      			fileSystemWatcher.Path = "C:\\spy";
      			fileSystemWatcher.NotifyFilter = NotifyFilters.LastWrite;
      			
      			fileSystemWatcher.Filter = "*.txt";
      			fileSystemWatcher.Changed += new FileSystemEventHandler(OnChanged);
      			fileSystemWatcher.EnableRaisingEvents = true;
      			Console.Write("Listening for changes in 'C:\\spy' directory...press any key to exit");
      			Console.Read();
      			
      		}
      		
      		private static void OnChanged(object source, FileSystemEventArgs e) {
      			Console.Write("\r\nFile: {0} {1} {2}", e.FullPath, e.ChangeType, DateTime.Now);
      		}
      	}
      }
      
      
    9. How to write the name of a calling function.

      Use the handy StackTrace object as shown below. Note: the write() method is defined elsewhere.

      ...
       using System.Diagnostics;
      ...
      /// <summary>
       /// writes the name of the method that called it
       /// </summary>
      
       public void writeMethodStart() {
      	   StackTrace stackTrace = new StackTrace();
      	   StackFrame stackFrame = stackTrace.GetFrame(1);
      	   MethodBase methodBase = stackFrame.GetMethod();
      	   write("Method who called me was \""+methodBase.Name+"\"");
       }
            
      
    10. Get the contents of a web page as a string

      /// <summary>
      /// returns the contents of the webpage whose url is passed in
      /// No error handling is done.  If something goes wrong an exception is thrown even
      /// something as simple as not being able to close the connection.
      /// </summary>
      /// <param name="link">url to get</param>
      
      /// <returns>string of web contents</returns>
      private static string GetWebPage(string link) {
          HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create(link);
          myRequest.Method = "GET";
          WebResponse webResponse = myRequest.GetResponse();
          StreamReader streamReader = new StreamReader(webResponse.GetResponseStream(), System.Text.Encoding.UTF8);
          string contents = streamReader.ReadToEnd();
          streamReader.Close();
          webResponse.Close();
          return contents;
      }
      
      
    11. To force .Net to use a proxy connection for web calls

      Add this to your web.config (inside the configuration element)

      <system.net>
         <defaultProxy>
      
            <proxy
               proxyaddress = "10.33.19.14:80"
               bypassonlocal = "true"
            />
         </defaultProxy>
      </system.net>
      
    12. How to bypass System.Web.UI.Page and write directly to requestor

      This is very useful in returning raw xml for AJAX invocations.

      using System;
      using System.Web;
       
      namespace RestDB {
      /// <summary>
      
      /// Example of using HttpHandler
      /// </summary>
      public class Rest : IHttpHandler {
      	public void ProcessRequest(HttpContext context) {
      		context.Response.Write("<h1>Houston we have contact!</h1>");
      	}
      	public bool IsReusable {
      		get { return true; }
      	}
      }
      }
      

      Add this snippet to your web.config

      <httpHandlers>
         <add verb="*" path="RestDB/*.aspx" type="RestDB.Rest,RestDB" />
      
      </httpHandlers> 
      
    13. How to write a gif to a browser request for an img tag

      This is useful when you need to know if a particular page has been viewed. Logic for recording the event is done elsewhere and then calls this routine.

      /// <summary>
      /// writes a gif image to the browser and closes the response object
      /// </summary>
      /// <param name="response">where to write the gif</param>
      
      /// <param name="absolutePath">where to read the gif</param>
      public static void WriteGif(System.Web.HttpResponse response,
      	string absolutePath) {
      	//TODO: cache images in hashmap with filename the key
      	FileStream fileStream;
      	long length = 0;
      
      	fileStream = new FileStream(absolutePath, FileMode.Open, FileAccess.Read);
      	length = fileStream.Length;
      
      	byte[] bBuffer = new byte[(int)length];
      	fileStream.Read(bBuffer, 0, (int)length);
      	fileStream.Close();
      
      	response.ClearContent();
      	response.ContentType = "image/gif";
      	response.BinaryWrite(bBuffer);
      	response.End();
      }
      
      
    14. Quick 'web service' call without the overhead

      If you only have a string to transmit between your server and client, you can cheat and use the "Response.StatusDescription" to pass a string message. In the Page_Load method of the server set the StatusDescription field of the Response object.

      private void Page_Load(object sender, System.EventArgs e) {
      ....
      Response.StatusDescription = "my tiny bit of information to transmit";
      ...
      }
      

      In the client, invoke a url on the server and look at the "StatusDescription" field for your tiny bit of info.

      string url = "http://...(your url goes here).......";
      HttpWebResponse resp = (HttpWebResponse)WebRequest.Create(url).GetResponse();
          
      string secretMessage = resp.StatusDescription; 
      
      
    15. How to add a javascript callback to an asp:checkbox.

      Unfortunately you can't simply add it in the HTML code. You have to go to the code behind page.

      private void Page_Load(object sender, System.EventArgs e)
      {
        if(!this.IsPostBack) {
          this.myCheckBox.Attributes.Add("onclick","javascript:myFunction()");
        }
      }
      
    16. Using cookies to set widget values

      private void Page_Load(object sender, System.EventArgs e)
      {
      	if(!this.IsPostBack) {
      		if(Request.Cookies["ExtraUrlParamsTextBox"] != null) {
      			ExtraUrlParamsTextBox.Text = Request.Cookies["ExtraUrlParamsTextBox"].Value;
      		}
      
      	}
      	if(this.IsPostBack) {
      		Response.Cookies["ExtraUrlParamsTextBox"].Value = ExtraUrlParamsTextBox.Text;
      	}
      }
      
    17. Setting a Cookie

      HttpCookie myCookie = new HttpCookie("myName");
      myCookie.Value = groupDropDown.SelectedItem.Text;
      myCookie.Expires = DateTime.Now.AddMonths(6);
      Response.Cookies.Add(myCookie);
      
    18. Getting a Cookie

      if (Request.Cookies["myName"] != null)
      {
      	itemSelected = Request.Cookies["myName"].Value;
      }
      
      
      
    19. Using standalone C# in an aspx page

      When a respondent is forwarded to this page, they are redirected to another page based on the value of "x" All their GET parameters are passed on as well. If x=ABCDE, then they are forwarded to ABCDE.html

      <%@ Page Language="C#" %>
      <script runat="server">
          protected void Page_Load(object sender, EventArgs e) {
              string source = Page.Request.QueryString["x"];
              if (string.IsNullOrEmpty(source)) {
                  source = "XYZ"; //this is the default source if nothing is passed in as "x" param
              }
              Page.Response.Redirect(source + ".html?" + Page.Request.QueryString);
          }
      </script>
      <html xmlns="http://www.w3.org/1999/xhtml" >
      <head runat="server">
          <title>Redirect Page</title>
      </head>
      <body>
      </body>
      </html>
      
  107. Misc Notes:
    1. To view an assembly in gui using a tree structure use the handy Intermediate Language Disassembler (ildasm):
      c:\...\bin>ildasm myassemblyname.dll
    2. To do a case-insensitive search for a string in a List<string> collection

    3. List Groups = new List();
      ...
      public bool IsGroupVisibleToUser(string groupName)
      {
         return Groups.FindIndex(x => x.Equals(groupName,
             StringComparison.OrdinalIgnoreCase)) != -1;
      }
      
      
    4. Which data type should we use for money?

      The "decimal" struct gives 28 significant digits and may be used for most currency applications. Use the "m" suffix for constants.

      const decimal interestRate = 0.02m;
      decimal interestEarned = customer.Amount*interestRate/365.25m;
      
    5. Dotnetfx.exe

      If your target machine may not have .Net installed, you can install Dotnetfx.exe during your program's installation and Dotnetfx will install the .Net framework.

    6. machine.config

      'machine.config' control's the settings for ASP.Net. It is found in a directory like "C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\CONFIG".

    7. To allow remote testing of web services

      For security reasons, only clients on the local host can access the web page version of a web service. To allow any client to access the service, put the following in the web.config inside the "system.web" element. This gets rid of the "The test form is only available for requests from the local machine." message.

      <!-- to allow remote access to web services -->
           <webServices> 
              <protocols>
      
                  <add name="HttpSoap1.2"/>
                  <add name="HttpSoap"/>
                  <add name="HttpGet"/> 
                  <add name="HttpPost"/> 
              </protocols> 
          </webServices> 
      
      
    8. Use stringBuilder.AppendFormat() instead of .Append() when doing multiple Appends.

      StringBuilder sb = new StringBuilder();
      const string first = "Odysseus";
      const string second = "Hector";
      //instead of this
      sb.Append(first).Append(" said, '").Append(second).Append(", it was his cousin.'");
      Console.Out.WriteLine(sb.ToString());
      sb = new StringBuilder();
      //use AppendFormat()
      sb.AppendFormat("{0} said, '{1}, it was his cousin.'",first,second);
      Console.Out.WriteLine(sb.ToString());
      

      Produces:

      Odysseus said, 'Hector, it was his cousin.'
      Odysseus said, 'Hector, it was his cousin.'
      
    9. The Main method can take 3 forms: "static void Main()","static int Main()",or "static int Main(string[] args)"
    10. Typical output: "System.Console.WriteLine("Howdy World!");"
    11. In VS.NET, to get the docs on an object, highlight it and press 'F1'
    12. To launch the Object Browser: View/Other Windows/Object Browser or Ctl-Alt-J
    13. To add namespaces to the object browser, in the Solution Explorer, right click on the "References" tag and select "Add..."
    14. Using an "@" in front of a string turns off escape substitutions, e.g.,, @"C:\ " == "C:\\ "
    15. Three ways to initialize an array

      int [] a = new int[10]; a[0] = 1; a[1] = 2;
      int [] b = new int[] { 1, 2 };
      int [] c = { 1, 2 };
    16. Our old friends, 'Preprocessor' commands, are available

      #if (DEBUG)
      ....
      #endif
      
      #warning remove next debug line from the code before release
      Console.Error.WriteLine("userID:"+userID+" : "+To.ToText(someObject));
      
      
    17. The 'checked' and 'unchecked' operators are used to turn on and off arithmetic exceptions, e.g.,, int x = unchecked(a * b);
    18. Enumerations (enum)
       
      enum Sizes {Tall, Grande, Venti};  //by default assigned to 0,1,2
      enum Sizes {Tall=1, Grande=2, Venti=4}; // can be overridden
      enum Sizes : byte {Tall, Grande, Venti}; //specify the size of the enum
      

      Enums in C# are well developed and have many interesting methods. Enums derive from System.Enum which contain methods like Format() and GetName(). GetValues() will return all the possible values of an enum.

      By default int values are assigned starting with zero. You can use powers of two to create combinable flags that can be used for bitwise operations like "&" and "|".

      [Flags]
      public enum MovieGenres
      {
          Comedy = 0, Drama = 1, SciFi = 2, Fantasy = 4, Documentary = 8
      }
      
    19. Struct

      Structures are similar to classes but do not have inheritance and, although created with the 'new' operator, they live on the stack.

    20. "using" keyword

      Ambiguity with class names may be resolved by the "using" keyword.

      
      using Set = MyUtil.Set;
      

      This tells the compiler that all instances of 'Set' in the rest of the file are references to 'MyUtil.Set'. This would be helpful if 'Set' becomes a real collection class in a future release of .Net and you have coded your own.

    21. "readonly" and "const" keywords
      public const string myValue = "abc"; //myValue cannot be changed.  Set at compile time.
      public readonly string myFutureValue; //this can be set only once at declaration or in the constructor
      

      const is set at compile time, and readonly at runtime.

    22. "is" keyword

      tests to determine if an object is of a particular type

      if(myShape is Circle) {
      ...
      }
      
    23. "as" keyword

      similar to a type cast, but if the object is not what is expected, "as" returns a null while a type cast throws an exception. It does not perform custom type conversions.

      Circle c = myShape as Circle;
      if(c != null) {
      ...
      }
      
    24. "base" is similiar, but not identical to, Java's "super" to access a parent's members.
    25. To read a double from a string: Console.Out.WriteLine("d = {0}",Double.Parse("1.02"));
    26. Use "sealed" as a method modify so no subclass can extend the class ( like java's "final")
    27. The Object class has four methods: ToString(), Equals(), GetHashCode(), and GetType(). The first two should be overridden. Example,
      
      public override string ToString() { return "I'm a Jet"; }
      
    28. Member Accessibility
      1. public - available to all code
      2. protected - accessible only from derived classes
      3. private - accessible only from within the immediate class
      4. internal - accessible only from within the same assembly
      5. protected internal - accessible only from within the same assembly or from classes extending classes from this assembly

      In addition to these Access Modifiers, the '[assembly: InternalsVisibleTo ("Friend")]' allows access to members from other assemblies, like testing code.

    29. Instead of using Java's "instanceof", C# uses the "is" operator. The "as" operator in C# is somewhat similar, but does more work.
  108. Installing a Service via Nant

    Hate typing in username and passwords? Let Nant do the work for you

    <target name="uninstall">
      <echo message="uninstalling..." />
      <exec program="installUtil.exe"
            basedir="C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727" 
            workingdir="C:\workfiles\throttler\src\Harvester\bin\debug"
            commandline="/u Harvester.exe"
            failonerror="false"
            />
    
    </target>
    
    <target name="install" depends="uninstall"  >
      <echo message="installing..." />
      <exec program="installUtil.exe"
            basedir="C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727" 
            workingdir="C:\workfiles\throttler\src\Harvester\bin\debug"
            commandline="/user=mydomain\myuser /password=mypassword Harvester.exe"
            />
    </target>
    

    Inside the installer program, read the values

    /// <summary>
    /// Sets the username and password for the service
    /// </summary>
    /// <param name="savedState"></param>
    protected override void OnBeforeInstall(IDictionary savedState)
    {
        base.OnBeforeInstall(savedState);
        this.serviceProcessInstaller1.Username =
            this.Context.Parameters["user"].ToString();
        this.serviceProcessInstaller1.Password =
            this.Context.Parameters["password"].ToString();
    
        this.serviceProcessInstaller1.Account =
            System.ServiceProcess.ServiceAccount.User;
    }
    
    
  109. Using Nullable Types

    In C# 2.0 we can use nullable types which are like regular objects but have a "HasValue()"

    using System;
    class Nullable {
        static void Main() {
            int? i = null;
            Console.Out.WriteLine("i = " + i);
            Console.Out.WriteLine("i.HasValue=" + i.HasValue);
            i = 6;
            Console.Out.WriteLine("i = " + i);
            Console.Out.WriteLine("i.HasValue=" + i.HasValue);
            Console.In.Read();
        }
    }
    
  110. How to surpress warning with MSBuild

    With csc.exe it's easy to surpress warning with the "nowarn" option. With MSBuild it's a little trickier. Use the "property" switch and encluse your warning numbers with "&quot;", which is a little awkward.

    <target name="compile">
        <exec program="MSBuild.exe" basedir="${framework::get-framework-directory(framework::get-target-framework())}" workingdir="${project::get-base-directory()}" commandline="MyProject.sln /verbosity:diag /p:Configuration=${string::to-upper(project.config)} /t:Clean;Rebuild /property:nowarn=&quot;1591,0618&quot;" output="MyProjectMSBuild.txt" />
      </target>
    
  111. How to write a message to the Event Log

    This tiny helper function creates the entry and closes it. The "source" argument is the name of your application

    ...
    WriteMessage("MyProgram",e.ToString(),System.Diagnostics.EventLogEntryType.Error);
    ...            
    private static void WriteMessage(string source, string message, System.Diagnostics.EventLogEntryType type) {
        System.Diagnostics.EventLog oEV = new System.Diagnostics.EventLog();
        oEV.Source = source;
        oEV.WriteEntry(message, type);
        oEV.Close();
    }
    
    
  112. Using generics in a list.

    Our old friendly collection, ArrayList, is alas not in Generics. Instead we use the List collection.

    using System.Collections.Generic;
    ...
    public List<XmlObject> GetChildren(string typeName) {
         List<XmlObject> list = new List<XmlObject>();
         foreach (XmlObject xmlObject in Children) {
             if (xmlObject.GetType().ToString()
                 == (NameSpace + typeName)) {
                 list.Add(xmlObject);
             }
         }
         return list;
     }
    
    
  113. Create your own generic class

    By adding "lt;T>" after the class you can create a Templated, or generic, version of your object, in this case a wrapper for cached items that have their creation date associated with them so they can be flushed later. We don't have to create a CachedItemString and a CachedItemInt.

    using System;
    
    namespace PlayingAround {
        class Cacher<T> {
                    public T CachedItem;
                    public DateTime ExpirationDate;
        }
        class Runner {
            private static void Main() {
                Cacher<string> myString = new Cacher<string>();
                myString.CachedItem = "old string";
                Console.Out.WriteLine("myString.CachedItem = {0}", myString.CachedItem);
                Cacher<int> myInt = new Cacher<int>();
                myInt.CachedItem = 6;
                Console.Out.WriteLine("myInt = {0}", myInt.CachedItem);
                Console.Out.Write("press return to exit."); Console.In.ReadLine();
            }
        }
    }
    

    Type parameters can only be used in methods and types - not in constructors or properties, etc...

    It is only by convention we use "T" as the name of the type, there is no magic in the name. When using multiple generic types, the convention is to make them more descriptive and start with a "T", e.g., "Node".

    "Open Type" generics have their type still unknown like "Stack", once bound to a type like "Stack" it is called a "Closed Type". During compilation all open types are converted to closed types.

  114. Create Generic Methods

    Methods can define their own generic types in their argument list. Note that when calling "Swap(...)" that the type is not needed since the types are infered from the arguments themselves.

    public static void Swap<T>(ref T first, ref T second)
    {
        T temp = first;
        first = second;
        second = temp;
    }
    private static void Main()
    {
        int x = 1, y = 2;
        Console.Out.WriteLine("x = {0}, y={1}",x ,y);
        Swap(ref x,ref y);
        Console.Out.WriteLine("x = {0}, y={1}", x, y);
    }
    
  115. Generic Constraints

    You can restrict the types used in Generics using "where"

    private class Animal{}
    private interface IPlant{}
    
    class ZooSpecimen<T> where T : Animal{}
    class BotanicalGardenSpecimen<T> where T : IPlant{}
    

    Constraints may be based on types, interfaces, clsses, struct, a previously defined type ("Naked type constraint"), or if the type has a parameterless constructor ( "where T : new()").

  116. Subclassing Generics

    A Generic class can be subclassed. The subclass may leave the type open, or as shown below, it may close the type.

    private class Animal{}
    private class Reptile : Animal {} 
    
    class ZooSpecimen<T> where T : Animal{}
    class HerpatariumSpecimen<T> : ZooSpecimen<Reptile> {}
    
  117. Get the current directory of an executing program if running as a service

    System.AppDomain.CurrentDomain.SetupInformation.ApplicationBase.ToString()
    
    or
    new System.IO.FileInfo(Assembly.GetCallingAssembly().Location).Directory.ToString()
    
  118. Examples of using Regular Expressions
    1. Remove unwelcome characters from a string

      string dirty = "asdf<<>>xyz";
      Regex regX = new Regex(@"([<>""'%;()&])");
      string clean =  regX.Replace(dirty, "");
      

      Remove all non-alphanumeric characters

      string clean = Regex.Replace(dirty, @"[\W]", "");
      
    2. Testing if each line in a data file conforms to a regular expression
    3. Regex regX = new Regex(@"([<>""'%;()&])");
          return regX.Replace(thisInput, "");
      
      private bool TestPanelistFile(TextWriter textWriter, string fileName) {
      	textWriter.WriteLine("Testing "+fileName);
      	StreamReader sr = new StreamReader(fileName);
      	//example line:
      	//"LUK09","g9002827491","DJH4W","Stopped By Signal","01/06/2006"
      	System.Text.RegularExpressions.Regex exp = 
      		new System.Text.RegularExpressions.Regex(
      		"\"[a-zA-Z0-9]+\",\"[a-zA-Z0-9]+\",\"[a-zA-Z0-9]+\",\"(Completed Successfully|Stopped By Signal)\",\"\\d\\d/\\d\\d/\\d\\d\\d\\d\""
      		);
      	int i=0;
      	string line = "";
      	while((line = sr.ReadLine()) != null) {
      		i++;
      		if( ! exp.IsMatch(line)) {
      			textWriter.WriteLine("\r\nError in input file on line "+i);
      			textWriter.WriteLine("  bad line: "+line);
      		} else {
      			if(i % 500 == 0) { textWriter.Write("."); }
      		}
      	}
      	return false;
      }
      
      
    4. Loop over matches

      /// <summary>
      /// takes a sql string with @parameters 
      /// ( SELECT * FROM table WHERE name = @name and lang = @lang) 
      /// and returns a string array with the names of all the parameters 
      /// e.g.,  {"name","lang"}
      /// </summary>
      /// <param name="cmd">sql string with '@' prefacing parameters</param>
      
      /// <returns>array like, {"name","lang"}</returns>
      private static string[] GetVariables(string cmd)
      {
          Regex rexp =new Regex("@[a-zA-Z0-9]+");
          MatchCollection matches = rexp.Matches(cmd);
          string[] strings = new string[matches.Count];
          for(int i=0;i<matches.Count;i++) {
          strings[i] = matches[i].ToString().Remove(0,1);
          }
      return strings;
      }
      
    5. Replace all characters that are not letters or numbers with "_".

      using System.Text.RegularExpressions;
      ...
      string filename = "file(1)";
      //find all characters that are not letters or numbers
      Regex regex = new Regex("[^a-zA-Z0-9]");
      filename = regex.Replace(filename, "_");
      
    6. Replace substring matches

      /// <summary>
      /// converts between the old style sql commands and parameterized.
      /// changes '$(xyz)' to @xyz.  e.g., "'$(name)'" returns "@name"
      /// 
      /// </summary>
      
      /// <param name="cmd">string to translate</param>
      /// <returns>string with updated params</returns>
      public static string ReplaceWithParameterizedArgs(string cmd) {
        Regex rexp = new Regex("'\\$\\(([a-zA-Z0-9]+)\\)'");
      # this replaces the entire match with the inner match only
        string result = rexp.Replace(cmd, "@$1");
        return result;
      }
      
      ...
      
      [Test]
      public void ReplaceWithParameterizedArgs() {
        writeMethodStart(MethodBase.GetCurrentMethod().ToString());
        Assert.AreEqual("@name   @test", 
          Util.ReplaceWithParameterizedArgs("'$(name)'   '$(test)'"));
        Assert.AreEqual("SELECT * FROM mytable where name = @name",
          Util.ReplaceWithParameterizedArgs("SELECT * FROM mytable where name = '$(name)'"));
        Assert.AreEqual("", Util.ReplaceWithParameterizedArgs(""));
      }
      
    7. Select a string

      This lifts the database name from a connection string.

      string result="No Database found.";
      Regex pattern = new Regex(@"Database=(?<databaseName>\w+)", RegexOptions.IgnoreCase);
      Match match = pattern.Match("Server=.; Integrated Security=SSPI; Database=T800; Application Name=Cyberdyne");
      if (match.Success) {
          result = match.Groups["databaseName"].Value;
      }
      
    8. Variables with the same name as keywords must start with an "@"

      An identifier with an "@" prefix is called a verbatim identifier.

      var @abstract = "My variable"; //although "abstract" is a keyword, we can use as a regular identifier
      
    9. Visual Studio Regular Expression Editing tips

      VS provides regular expressions in replacing string which can be a lifesaver. Here's a few examples of operations to be performed on many files:

      1. Removing an xml attribute

        What the RE means: Find the string "<Survey " followed by a bunch of characters, followed by the string "cluster=" followed by a bunch of non-space characters. Replace with just the "<Survey " and the characters before "cluster".

        regex:  to delete the attribute "cluster" from the "Survey" element:
        Find What: \<Survey {.*} cluster=[^ ]*
        Replace With: \<Survey \1
        
      2. Rename an attribute

        In this case I want to rename the "Survey" element's 'id' attribute to 'registrarId', but not the other elements' 'id' attribute. The element name and the attribute to change must be on the same line for this to work. A tiny sliver of regular expression in the "Find and Replace" dialog did the trick: The "Find What" says find "<Survey " followed by any characters followed by " id=". The "\1" takes the value of all the characters skipped with the {.*}.
        Find What:  \<Survey {.*} id=
        Replace with: \<Survey \1 registrarId=
        
        
  119. How to get the version number of your assembly?

    This will print the version set in Properties/AssemblyInfo.cs.

    Console.WriteLine("version:"+Assembly.GetExecutingAssembly().GetName().Version.ToString());
    
  120. Finalize

    C# provides a way to release resources when an object dies. Like in C++, the destructor has the same name as the class with a "~" prefix.

    using System;
    public class Destructo {
    	~Destructo() {
    		Console.WriteLine("Help, I'm being destroye.#@@!@##");
    	}
    	public static void Main(string[] args) {
    		new Destructo();
    		new Destructo();
        }
    }
    

    This produces the following, but not reliably since the Console.Out may have been closed by then.

                Help, I'm being destroye.#@@!@##
                Help, I'm being destroye.#@@!@##
    
  121. CLSCompliant

    Using the CLSCompliant(true) attribute marks the assembly as being Common Language Specification compliant, so VB and other .Net languages can use your assembly. When compiling with this attribute, the compiler warns you with the error message CS3008 of non-compliant issues like exposed variable names differing only in case.

    ...
    using System.Xml;
    
    [assembly: CLSCompliant(true)]
    namespace MyComponents {
    
  122. Using Regular Expressions in Visual Studio for Replacing text

    If you have lots of test xml files for creating objects and you need to add a new attribute, it's easy with regular expressions. For example, if you need to add "newattribute='1'" to all "Survey" elements scattered over many files like this one:

    <Survey name='MoonManA' groupName='Baseline' priority='1' status='1' cellLimiter='100' surveyLimiter='100' dateStart='2004-01-10T08:00:00' dateEnd='2007-10-30T16:30:00' exclusions='0' cluster='Cluster1' >
    

    Enter "control-h" to bring up the Replace dialogue box and select the "Use:" check box in the lower left corner and make sure it displays "Regular expressions". Then enter these:

    "Find what:" \<Survey {[^\>]*}\>
    "Replace with:" <Survey  \1newattribute='0'>
    
    

    This will match all characters between "<Survey" and the ">". Putting the expression in braces allows you to use the "\1" syntax to place in the matched characters. The final result is

    <Survey name='MoonManA' groupName='Baseline' priority='1' status='1' cellLimiter='100' surveyLimiter='100' dateStart='2004-01-10T08:00:00' dateEnd='2007-10-30T16:30:00' exclusions='0' cluster='Cluster1' newattribute='0' >
    
    
  123. Delegates

    Delegates are type-safe function pointers. In the old C# 1.0 days a delegate method had to have it's own declaration as a method like this:

    // CalculateTax is a delegate that takes a double and returns a double
    public delegate double CalculateTax(double x);
    static public double StateTax(double x) { 
       return x * 0.05; 
       }
    static public double FederalTax(double x) { 
       if (x > 1000.0) 
          return x * 0.02; 
       else 
       return 0.0; 
    }
    
    static void Main(string[] args) {
    CalculateTax stateDelegate = new CalculateTax(StateTax);
    CalculateTax federalDelegate = new CalculateTax(FederalTax);
    double amountOfPurchase = 12.99;
    Console.WriteLine("{0}", stateDelegate(amountOfPurchase));
    Console.WriteLine("{0}", federalDelegate(amountOfPurchase));
    
    Console.In.ReadLine();
    }
    
    
  124. Anonymous methods (C# 2.0)

    You can do the same as above with a cleaner look by using anonymous methods. We don't have to declare a real method, we can just inline it:

    // CalculateTax is a delegate that takes a double and returns a double
    public delegate double CalculateTax(double x);
    static void Main(string[] args) {
        CalculateTax stateDelegate = delegate(double x) { return x * 0.05; };
        CalculateTax federalDelegate = delegate(double x) { if (x > 1000.0) return x * 0.02; else return 0.0; };
        double amountOfPurchase = 12.99;
    
        Console.WriteLine("{0}", stateDelegate(amountOfPurchase));
        Console.WriteLine("{0}", federalDelegate(amountOfPurchase));
    
        Console.In.ReadLine();
    }
    
    
  125. ASP.NET notes

    Types of files

    1. .aspx.cs - web forms, like jsp pages
    2. .ascx.cs - c# code objects
    3. .asmx - web services
    4. .asax - global objects
    5. .ashx - http modules

    Three types of controls

    1. HTML server controls
    2. Web server controls
    3. Validation
  126. Notes on .NET. The Common Language Infrastructure (CLI) consists of 5 parts
    1. Partition I - Architecture
      1. Common Lanugage Specification (CLS)

        rules that guarantee one language can interoperate with others if it follows the specification

      2. Common Type System (CTS)
        Type
        1. Value Types
          1. Built-in Value Types
            1. Integer Types
            2. Floating Point Types
            3. Typed References
          2. User Defined
            1. Enums
      3. Virtual Execution System (VES)
    2. Partition II - Metadata
    3. Partition III - Common Intermediate Language (CIL) bytecode
    4. Partition IV - Library
    5. Partition V - Annexes
    < Prev  1 2 3 4 5  Next >

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