using System;
using System.Windows.Forms;
using System.Drawing;

public class Butevent:Form  {
TextBox t1 = new TextBox();
Button b1 = new Button();
public Butevent() {
this.Text = "C# Program ";
t1.Location = new Point(20,30);
b1.Text = "Click here to activate";
b1.Location = new Point(20,55);
b1.Size = new Size(150,20);

     // Invoking Method or EventHandler
     b1.Click+=new EventHandler(OnClick);

     this.Controls.Add(t1);
     this.Controls.Add(b1);

     // Invoking Method or EventHandler
     this.Resize += new EventHandler(OnResize);
   }

   //Applying EventHandler
   public void OnResize(object sender,EventArgs ee) {
      MessageBox.Show("oops! Form Resized");
   }

   //Applying EventHandler
   public void OnClick(object sender,EventArgs e) {
      t1.Text = "Hello C#";
   }

   public static void Main() {
      Application.Run(new Butevent());
   }

}

using System.Text.RegularExpressions;
The second step is to detect a URL:

Regex urlregex = new Regex(@"(http:\/\/([\w.]+\/?)\S*)",
   RegexOptions.IgnoreCase|RegexOptions.Compiled);

Here is how to detect an e-mail address:

Regex emailregex = new 
Regex(@"([a-zA-Z_0-9.-]+\@[a-zA-Z_0-9.-]+\.\w+)",
   RegexOptions.IgnoreCase|RegexOptions.Compiled);



private void Button1_Click(object sender, System.EventArgs 
e)
{
   string strContent = InputTextBox.Text;
   Regex urlregex = new Regex(@"(http:\/\/([\w.]+\/?)\S*)",
                    RegexOptions.IgnoreCase| 
RegexOptions.Compiled);
   strContent = urlregex.Replace(strContent,
                "");
   Regex emailregex = new 
Regex(@"([a-zA-Z_0-9.-]+\@[a-zA-Z_0-9.-]+\.\w+)",
      RegexOptions.IgnoreCase| RegexOptions.Compiled);
   strContent = emailregex.Replace(strContent, "");
   lbContent.Text += ""+strContent;
}

protected void TreeView1_SelectedNodeChanged(object sender, 
EventArgs e)
{
Label1.Text = "You Selected " + TreeView1.SelectedNode.Text
                                 + " category";
}
protected void Page_Load(object sender, EventArgs e)
{
   switch (Request.QueryString["id"])
   {
      case "1":
         Label1.Text="You selected ASP.NET category";
         break;
      case "2":
         Label1.Text="You selected Web Services category";
         break;
      case "3":
         Label1.Text="You selected JSP category";
         break;
      case "4":
         Label1.Text="You selected Windows Forms category";
         break;
      case "5":
         Label1.Text="You selected ActiveX category";
         break;
      case "6":
         Label1.Text="You selected Smart Client category";
         break;
      case "7":
         Label1.Text="You selected COM category";
         break;
      case "8":
         Label1.Text="You selected DCOM category";
         break;
      case "9":
         Label1.Text = "You selected Remoting category";
         break;
   }
}

Microsoft.Web.UI.WebControls.TreeView Treeview11 

public void PopulateTree()
{
   TreeNode nodeProdDetail, nodeProdMaster;
   nodeProdMaster      = new TreeNode();
   nodeProdMaster.Text = "Master1";
   nodeProdMaster.ID   = "1";

   nodeProdDetail             = new TreeNode();
   nodeProdDetail.Text        = "Detail1";
   nodeProdDetail.ID          = "1.1";
   nodeProdDetail.NavigateUrl = "SomePage.aspx";
   nodeProdMaster.Nodes.Add(nodeProdDetail);

   Treeview1.Nodes.Add(nodeProdMaster);

   nodeProdMaster      = new TreeNode();
   nodeProdMaster.Text = "Master2";
   nodeProdMaster.ID   = "2";

   nodeProdDetail             = new TreeNode();
   nodeProdDetail.Text        = "Detail2";
   nodeProdDetail.ID          = "2.1";
   nodeProdDetail.NavigateUrl = "SomeOtherPage.aspx";
   nodeProdMaster.Nodes.Add(nodeProdDetail);

   Treeview1.Nodes.Add(nodeProdMaster);
}

public void AddConfirmMessage(WebControl ctl, string 
message)
{
   ctl.Attributes.Add("onclick", "if ( ! confirm( '"
      + message + "' )) return false; ");
}

public void AddPopupMessage(WebControl ctl, string message)
{
   ctl.Attributes.Add("onclick", "alert( '" + message 
+ "'); ");
}