delegate FROM MSDN

  //加重部分 定义代理
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace Calculator
{
 public class Form1 : System.Windows.Forms.Form
 {
  #region DETAILS...
  private System.Windows.Forms.Label label1;
  private System.Windows.Forms.Label label2;
  private System.Windows.Forms.TextBox txtNumber1;
  private System.Windows.Forms.Button cmdAdd;
  private System.Windows.Forms.TextBox txtNumber2;
  private System.Windows.Forms.Button cmdEnable;
  private System.Windows.Forms.Button cmdDisable;
  /// <summary>
  /// Required designer variable.
  /// </summary>
  private System.ComponentModel.Container components = null;

  public Form1()
  {
   //
   // Required for Windows Form Designer support
   //
   InitializeComponent();

   //
   // TODO: Add any constructor code after InitializeComponent call
   //
  }

  /// <summary>
  /// Clean up any resources being used.
  /// </summary>
  protected override void Dispose( bool disposing )
  {
   if( disposing )
   {
    if (components != null)
    {
     components.Dispose();
    }
   }
   base.Dispose( disposing );
  }

  #endregion

  #region Windows Form Designer generated code
  /// <summary>
  /// Required method for Designer support - do not modify
  /// the contents of this method with the code editor.
  /// </summary>
  private void InitializeComponent()
  {
   this.label1 = new System.Windows.Forms.Label();
   this.label2 = new System.Windows.Forms.Label();
   this.txtNumber1 = new System.Windows.Forms.TextBox();
   this.txtNumber2 = new System.Windows.Forms.TextBox();
   this.cmdAdd = new System.Windows.Forms.Button();
   this.cmdEnable = new System.Windows.Forms.Button();
   this.cmdDisable = new System.Windows.Forms.Button();
   this.SuspendLayout();
   //
   // label1
   //
   this.label1.Location = new System.Drawing.Point(24, 24);
   this.label1.Name = "label1";
   this.label1.Size = new System.Drawing.Size(120, 32);
   this.label1.TabIndex = 0;
   this.label1.Text = "Number 1:";
   //
   // label2
   //
   this.label2.Location = new System.Drawing.Point(24, 72);
   this.label2.Name = "label2";
   this.label2.Size = new System.Drawing.Size(120, 32);
   this.label2.TabIndex = 2;
   this.label2.Text = "Number 2:";
   //
   // txtNumber1
   //
   this.txtNumber1.Location = new System.Drawing.Point(152, 24);
   this.txtNumber1.Name = "txtNumber1";
   this.txtNumber1.Size = new System.Drawing.Size(160, 29);
   this.txtNumber1.TabIndex = 1;
   this.txtNumber1.Text = "";
   //
   // txtNumber2
   //
   this.txtNumber2.Location = new System.Drawing.Point(152, 72);
   this.txtNumber2.Name = "txtNumber2";
   this.txtNumber2.Size = new System.Drawing.Size(160, 29);
   this.txtNumber2.TabIndex = 3;
   this.txtNumber2.Text = "";
   //
   // cmdAdd
   //
   this.cmdAdd.Location = new System.Drawing.Point(168, 120);
   this.cmdAdd.Name = "cmdAdd";
   this.cmdAdd.Size = new System.Drawing.Size(128, 56);
   this.cmdAdd.TabIndex = 4;
   this.cmdAdd.Text = "Add";
   this.cmdAdd.Click += new System.EventHandler(this.cmdAdd_Click);
   //
   // cmdEnable
   //
   this.cmdEnable.CausesValidation = false;
   this.cmdEnable.Font = new System.Drawing.Font("Microsoft Sans Serif", 14.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0)));
   this.cmdEnable.Location = new System.Drawing.Point(24, 280);
   this.cmdEnable.Name = "cmdEnable";
   this.cmdEnable.Size = new System.Drawing.Size(272, 48);
   this.cmdEnable.TabIndex = 6;
   this.cmdEnable.TabStop = false;
   this.cmdEnable.Text = "Enable Validation";
   this.cmdEnable.Click += new System.EventHandler(this.cmdEnable_Click);
   //
   // cmdDisable
   //
   this.cmdDisable.CausesValidation = false;
   this.cmdDisable.Font = new System.Drawing.Font("Microsoft Sans Serif", 14.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0)));
   this.cmdDisable.Location = new System.Drawing.Point(24, 216);
   this.cmdDisable.Name = "cmdDisable";
   this.cmdDisable.Size = new System.Drawing.Size(272, 48);
   this.cmdDisable.TabIndex = 5;
   this.cmdDisable.TabStop = false;
   this.cmdDisable.Text = "Disable Validation";
   this.cmdDisable.Click += new System.EventHandler(this.cmdDisable_Click);
   //
   // Form1
   //
   this.AutoScaleBaseSize = new System.Drawing.Size(10, 22);
   this.ClientSize = new System.Drawing.Size(338, 352);
   this.Controls.AddRange(new System.Windows.Forms.Control[] {
                    this.cmdDisable,
                    this.cmdEnable,
                    this.cmdAdd,
                    this.txtNumber2,
                    this.txtNumber1,
                    this.label2,
                    this.label1});
   this.Font = new System.Drawing.Font("Microsoft Sans Serif", 14.25F, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0)));
   this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle;
   this.MaximizeBox = false;
   this.Name = "Form1";
   this.Text = "Calculator";
   this.Load += new System.EventHandler(this.Form1_Load);
   this.ResumeLayout(false);

  }
  #endregion

  [STAThread]
  static void Main()
  {
   Application.Run(new Form1());
  }

  private void cmdAdd_Click(object sender, System.EventArgs e)
  {
   int  num1, num2, result;

   num1 = int.Parse(this.txtNumber1.Text);
   num2 = int.Parse(this.txtNumber2.Text);

   result = num1 + num2;

   MessageBox.Show("The sum = " + result, "Calculator");
  }

  private void Form1_Load(object sender, System.EventArgs e)
  {
   this.txtNumber1.Validating += new System.ComponentModel.CancelEventHandler(Validation.IsInteger);
   this.txtNumber2.Validating += new System.ComponentModel.CancelEventHandler(Validation.IsInteger);

   // validation is already enabled, so prevent user from adding more validation handlers
   this.cmdEnable.Enabled = false; 
  }

  private void cmdDisable_Click(object sender, System.EventArgs e)
  {
   this.txtNumber1.Validating -= new System.ComponentModel.CancelEventHandler(Validation.IsInteger);
   this.txtNumber2.Validating -= new System.ComponentModel.CancelEventHandler(Validation.IsInteger);

   // toggle buttons so user can enable later...
   this.cmdDisable.Enabled = false;
   this.cmdEnable.Enabled  = true;
  }

  private void cmdEnable_Click(object sender, System.EventArgs e)
  {
   this.txtNumber1.Validating += new System.ComponentModel.CancelEventHandler(Validation.IsInteger);
   this.txtNumber2.Validating += new System.ComponentModel.CancelEventHandler(Validation.IsInteger);

   // toggle buttons so user can disable later...
   this.cmdEnable.Enabled  = false;
   this.cmdDisable.Enabled = true;
  }

 }
}

//定义代理函数
using System;
using SWF = System.Windows.Forms;

namespace Calculator
{

 public class Validation
 {

  public static void IsInteger(object sender, System.ComponentModel.CancelEventArgs e)
  {
   SWF.TextBox  txt;
   txt = (SWF.TextBox) sender;

   try
   {
    int.Parse(txt.Text);
   }
   catch(FormatException)
   {
    SWF.MessageBox.Show("Please enter a numeric value.", "Calculator");
    e.Cancel = true;  // cancel validation, returns focus
   }
   catch(OverflowException)
   {
    SWF.MessageBox.Show("Please enter an integer in the range " + int.MinValue + " ... " + int.MaxValue, "Calculator");
    e.Cancel = true;  // cancel validation, returns focus
   }
   catch(Exception ex)
   {
    SWF.MessageBox.Show("Unknown error: " + ex.Message, "Calculator");
    e.Cancel = true;  // cancel validation, returns focus
   }
  }
 
 }//class
}//namespace