Imports System
Imports System.ComponentModel
Imports System.Threading
Imports System.Windows.Forms

Public Class Form1
   Inherits Form

   ' This delegate enables asynchronous calls for setting
   ' the text property on a TextBox control.
   Delegate Sub SetTextCallback([text] As String)

   ' This thread is used to demonstrate both thread-safe and
   ' unsafe ways to call a Windows Forms control.
   Private demoThread As Thread = Nothing

   ' This BackgroundWorker is used to demonstrate the 
   ' preferred way of performing asynchronous operations.
   Private WithEvents backgroundWorker1 As BackgroundWorker

   Private textBox1 As TextBox
   Private WithEvents setTextUnsafeBtn As Button
   Private WithEvents setTextSafeBtn As Button
   Private WithEvents setTextBackgroundWorkerBtn As Button

   Private components As System.ComponentModel.IContainer = Nothing


   Public Sub New()
      InitializeComponent()
    End Sub


   Protected Overrides Sub Dispose(disposing As Boolean)
      If disposing AndAlso (components IsNot Nothing) Then
         components.Dispose()
      End If
      MyBase.Dispose(disposing)
    End Sub


   ' This event handler creates a thread that calls a 
   ' Windows Forms control in an unsafe way.
    Private Sub setTextUnsafeBtn_Click( _
    ByVal sender As Object, _
    ByVal e As EventArgs) Handles setTextUnsafeBtn.Click

        Me.demoThread = New Thread( _
        New ThreadStart(AddressOf Me.ThreadProcUnsafe))

        Me.demoThread.Start()
    End Sub


   ' This method is executed on the worker thread and makes
   ' an unsafe call on the TextBox control.
   Private Sub ThreadProcUnsafe()
      Me.textBox1.Text = "This text was set unsafely."
   End Sub 

   ' This event handler creates a thread that calls a 
   ' Windows Forms control in a thread-safe way.
    Private Sub setTextSafeBtn_Click( _
    ByVal sender As Object, _
    ByVal e As EventArgs) Handles setTextSafeBtn.Click

        Me.demoThread = New Thread( _
        New ThreadStart(AddressOf Me.ThreadProcSafe))

        Me.demoThread.Start()
    End Sub


   ' This method is executed on the worker thread and makes
   ' a thread-safe call on the TextBox control.
   Private Sub ThreadProcSafe()
      Me.SetText("This text was set safely.")
    End Sub

   ' 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 Sub SetText(ByVal [text] As String)

        ' 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 Me.textBox1.InvokeRequired Then
            Dim d As New SetTextCallback(AddressOf SetText)
            Me.Invoke(d, New Object() {[text]})
        Else
            Me.textBox1.Text = [text]
        End If
    End Sub

   ' 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 Sub setTextBackgroundWorkerBtn_Click( _
    ByVal sender As Object, _
    ByVal e As EventArgs) Handles setTextBackgroundWorkerBtn.Click
        Me.backgroundWorker1.RunWorkerAsync()
    End Sub


   ' 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 Sub backgroundWorker1_RunWorkerCompleted( _
    ByVal sender As Object, _
    ByVal e As RunWorkerCompletedEventArgs) _
    Handles backgroundWorker1.RunWorkerCompleted
        Me.textBox1.Text = _
        "This text was set safely by BackgroundWorker."
    End Sub

   #Region "Windows Form Designer generated code"


   Private Sub InitializeComponent()
      Me.textBox1 = New System.Windows.Forms.TextBox()
      Me.setTextUnsafeBtn = New System.Windows.Forms.Button()
      Me.setTextSafeBtn = New System.Windows.Forms.Button()
      Me.setTextBackgroundWorkerBtn = New System.Windows.Forms.Button()
      Me.backgroundWorker1 = New System.ComponentModel.BackgroundWorker()
      Me.SuspendLayout()
      ' 
      ' textBox1
      ' 
      Me.textBox1.Location = New System.Drawing.Point(12, 12)
      Me.textBox1.Name = "textBox1"
      Me.textBox1.Size = New System.Drawing.Size(240, 20)
      Me.textBox1.TabIndex = 0
      ' 
      ' setTextUnsafeBtn
      ' 
      Me.setTextUnsafeBtn.Location = New System.Drawing.Point(15, 55)
      Me.setTextUnsafeBtn.Name = "setTextUnsafeBtn"
      Me.setTextUnsafeBtn.TabIndex = 1
      Me.setTextUnsafeBtn.Text = "Unsafe Call"
      ' 
      ' setTextSafeBtn
      ' 
      Me.setTextSafeBtn.Location = New System.Drawing.Point(96, 55)
      Me.setTextSafeBtn.Name = "setTextSafeBtn"
      Me.setTextSafeBtn.TabIndex = 2
      Me.setTextSafeBtn.Text = "Safe Call"
      ' 
      ' setTextBackgroundWorkerBtn
      ' 
      Me.setTextBackgroundWorkerBtn.Location = New System.Drawing.Point(177, 55)
      Me.setTextBackgroundWorkerBtn.Name = "setTextBackgroundWorkerBtn"
      Me.setTextBackgroundWorkerBtn.TabIndex = 3
      Me.setTextBackgroundWorkerBtn.Text = "Safe BW Call"
      ' 
      ' backgroundWorker1
      ' 
      ' 
      ' Form1
      ' 
      Me.ClientSize = New System.Drawing.Size(268, 96)
      Me.Controls.Add(setTextBackgroundWorkerBtn)
      Me.Controls.Add(setTextSafeBtn)
      Me.Controls.Add(setTextUnsafeBtn)
      Me.Controls.Add(textBox1)
      Me.Name = "Form1"
      Me.Text = "Form1"
      Me.ResumeLayout(False)
      Me.PerformLayout()
   End Sub 'InitializeComponent 

   #End Region

   <STAThread()>  _
   Shared Sub Main()
      Application.EnableVisualStyles()
      Application.Run(New Form1())
    End Sub
End Class

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());
		}

	}
}