// This event handler creates a thread that calls a 
  // Windows Forms control in an unsafe way.
  private void setTextUnsafeBtn_Click(
   object sender, 
   EventArgs e)
  {
   this.demoThread = 
    new Thread(new ThreadStart(this.ThreadProcUnsafe));
   this.demoThread.Start();
  }
  // This method is executed on the worker thread and makes
  // an unsafe call on the TextBox control.
  private void ThreadProcUnsafe()
  {
   this.textBox1.Text = "This text was set unsafely.";
  }

// This event handler creates a thread that calls a 
  // Windows Forms control in a thread-safe way.
  private void setTextSafeBtn_Click(
   object sender, 
   EventArgs e)
  {
    this.demoThread = 
    new Thread(new ThreadStart(this.ThreadProcSafe));
    this.demoThread.Start();
  }

  // This method is executed on the worker thread and makes
  // a thread-safe call on the TextBox control.
  private void ThreadProcSafe()
  {
   this.SetText("This text was set safely.");
  }

using System;
using System.ComponentModel;
using System.Threading;
using System.Windows.Forms;

namespace CrossThreadDemo
{
 public class Form1 : Form
 {
  // This delegate enables asynchronous calls for setting
  // the text property on a TextBox control.
  delegate void SetTextCallback(string text);

  // This thread is used to demonstrate both thread-safe and
  // unsafe ways to call a Windows Forms control.
  private Thread demoThread = null;

  // This BackgroundWorker is used to demonstrate the 
  // preferred way of performing asynchronous operations.
  private BackgroundWorker backgroundWorker1;

  private TextBox textBox1;
  private Button setTextUnsafeBtn;
  private Button setTextSafeBtn;
  private Button setTextBackgroundWorkerBtn;

  private System.ComponentModel.IContainer components = null;

  public Form1()
  {
   InitializeComponent();
  }

  protected override void Dispose(bool disposing)
  {
   if (disposing && (components != null))
   {
    components.Dispose();
   }
   base.Dispose(disposing);
  }

  // This event handler creates a thread that calls a 
  // Windows Forms control in an unsafe way.
  private void setTextUnsafeBtn_Click(
   object sender, 
   EventArgs e)
  {
   this.demoThread = 
    new Thread(new ThreadStart(this.ThreadProcUnsafe));

   this.demoThread.Start();
  }

  // This method is executed on the worker thread and makes
  // an unsafe call on the TextBox control.
  private void ThreadProcUnsafe()
  {
   this.textBox1.Text = "This text was set unsafely.";
  }

  // This event handler creates a thread that calls a 
  // Windows Forms control in a thread-safe way.
  private void setTextSafeBtn_Click(
   object sender, 
   EventArgs e)
  {
   this.demoThread = 
    new Thread(new ThreadStart(this.ThreadProcSafe));

   this.demoThread.Start();
  }

  // This method is executed on the worker thread and makes
  // a thread-safe call on the TextBox control.
  private void ThreadProcSafe()
  {
   this.SetText("This text was set safely.");
  }

  // This method demonstrates a pattern for making thread-safe
  // calls on a Windows Forms control. 
  //
  // If the calling thread is different from the thread that
  // created the TextBox control, this method creates a
  // SetTextCallback and calls itself asynchronously using the
  // Invoke method.
  //
  // If the calling thread is the same as the thread that created
  // the TextBox control, the Text property is set directly. 

  private void SetText(string text)
  {
   // InvokeRequired required compares the thread ID of the
   // calling thread to the thread ID of the creating thread.
   // If these threads are different, it returns true.
   if (this.textBox1.InvokeRequired)
   { 
    SetTextCallback d = new SetTextCallback(SetText);
    this.Invoke(d, new object[] { text });
   }
   else
   {
    this.textBox1.Text = text;
   }
  }

  // This event handler starts the form's 
  // BackgroundWorker by calling RunWorkerAsync.
  //
  // The Text property of the TextBox control is set
  // when the BackgroundWorker raises the RunWorkerCompleted
  // event.
  private void setTextBackgroundWorkerBtn_Click(
   object sender, 
   EventArgs e)
  {
   this.backgroundWorker1.RunWorkerAsync();
  }
  
  // This event handler sets the Text property of the TextBox
  // control. It is called on the thread that created the 
  // TextBox control, so the call is thread-safe.
  //
  // BackgroundWorker is the preferred way to perform asynchronous
  // operations.

  private void backgroundWorker1_RunWorkerCompleted(
   object sender, 
   RunWorkerCompletedEventArgs e)
  {
   this.textBox1.Text = 
    "This text was set safely by BackgroundWorker.";
  }

  #region Windows Form Designer generated code

  private void InitializeComponent()
  {
   this.textBox1 = new System.Windows.Forms.TextBox();
   this.setTextUnsafeBtn = new System.Windows.Forms.Button();
   this.setTextSafeBtn = new System.Windows.Forms.Button();
   this.setTextBackgroundWorkerBtn = new System.Windows.Forms.Button();
   this.backgroundWorker1 = new System.ComponentModel.BackgroundWorker();
   this.SuspendLayout();
   // 
   // textBox1
   // 
   this.textBox1.Location = new System.Drawing.Point(12, 12);
   this.textBox1.Name = "textBox1";
   this.textBox1.Size = new System.Drawing.Size(240, 20);
   this.textBox1.TabIndex = 0;
   // 
   // setTextUnsafeBtn
   // 
   this.setTextUnsafeBtn.Location = new System.Drawing.Point(15, 55);
   this.setTextUnsafeBtn.Name = "setTextUnsafeBtn";
   this.setTextUnsafeBtn.TabIndex = 1;
   this.setTextUnsafeBtn.Text = "Unsafe Call";
   this.setTextUnsafeBtn.Click += new System.EventHandler(this.setTextUnsafeBtn_Click);
   // 
   // setTextSafeBtn
   // 
   this.setTextSafeBtn.Location = new System.Drawing.Point(96, 55);
   this.setTextSafeBtn.Name = "setTextSafeBtn";
   this.setTextSafeBtn.TabIndex = 2;
   this.setTextSafeBtn.Text = "Safe Call";
   this.setTextSafeBtn.Click += new System.EventHandler(this.setTextSafeBtn_Click);
   // 
   // setTextBackgroundWorkerBtn
   // 
   this.setTextBackgroundWorkerBtn.Location = new System.Drawing.Point(177, 55);
   this.setTextBackgroundWorkerBtn.Name = "setTextBackgroundWorkerBtn";
   this.setTextBackgroundWorkerBtn.TabIndex = 3;
   this.setTextBackgroundWorkerBtn.Text = "Safe BW Call";
   this.setTextBackgroundWorkerBtn.Click += new System.EventHandler(this.setTextBackgroundWorkerBtn_Click);
   // 
   // backgroundWorker1
   // 
   this.backgroundWorker1.RunWorkerCompleted += new System.ComponentModel.RunWorkerCompletedEventHandler(this.backgroundWorker1_RunWorkerCompleted);
   // 
   // Form1
   // 
   this.ClientSize = new System.Drawing.Size(268, 96);
   this.Controls.Add(this.setTextBackgroundWorkerBtn);
   this.Controls.Add(this.setTextSafeBtn);
   this.Controls.Add(this.setTextUnsafeBtn);
   this.Controls.Add(this.textBox1);
   this.Name = "Form1";
   this.Text = "Form1";
   this.ResumeLayout(false);
   this.PerformLayout();

  }

  #endregion


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

 }
}