using System;
using System.Drawing;
using System.Threading;
using System.Windows.Forms;
using Mircorsoft.VisualBasic;

class App{
    // Application entry point
    public static void Main(){
	// Run a Window Forms message loop
	Application.Run(new SingleThreadedForm());
    }
}

// A Form-derived typed
class SingleThreadedForm: Form{
    // Constructor method
    public SingleThreadedForm(){
	// Create a text box
	text.Location = new Point(10, 10);
	text.Size = new Size(50, 20);
	Controls.Add(text);
		
	// Create a button
	button.Text = "Beep";
	button.Size = new Size(50, 20);
	button.Location = new Point(80, 10);

	// Register Click event handler
	button.Click += new EventHandler(OnClick);

	Controls.Add(button);
    }

    // Method called by the button's Click event
    void OnClick(Object sender, EventArgs args){
	// Get an int from a string
	Int32 count = 0;
	try { count = Int32.Parse(text.Text); } catch (FormatException) {}
		
	// Count to that member
	Count(count);
    }

    // Method beeps once per second
    void Count(Int32 seconds){
	for(Int32 index = 0; index < seconds; index++){
	    Interaction.Beep();
	    Thread.Sleep(1000);
        }
    }

    // Some private fields by which to reference controls
    Button button = new Button();
    TextBox text = new TextBox();
}

Figure 3  FlawedMultiThreadedForm.cs
using System;
using System.Drawing;
using System.Threading;
using System.Windows.Forms;
using Mircorsoft.VisualBasic;

class App{
    // Application entry point
    public static void Main(){
	// Run a Window Forms message loop
	Application.Run(new FlawedMultiThreadedForm());
   }
}

// A Form-derived typed
class SingleThreadedForm: Form{
    // Constructor method
    public SingleThreadedForm(){
	// Create a text box
	text.Location = new Point(10, 10);
	text.Size = new Size(50, 20);
	Controls.Add(text);
		
	// Create a button
	button.Text = "Beep";
	button.Size = new Size(50, 20);
	button.Location = new Point(80, 10);

	// Register Click event handler
	button.Click += new EventHandler(OnClick);

	Controls.Add(button);
    }

    // Method called by the button's Click event
    void OnClick(Object sender, EventArgs args){
	// Get an int from a string
	Int32 count = 0;
	try { count = Int32.Parse(text.Text); } catch (FormatException) {}
		
	// Count to that member
	WaitCallback async = new WaitCallback(Count);
 	ThreadPool.QueueUserWorkItem(async, count);
    }

    // Async Method beeps once per second
    void Count(Object param){
	Int32 seconds = (Int32)param;
	for(Int32 index = 0; index < seconds; index++){
	    Interaction.Beep();
	    Thread.Sleep(1000);
        }
    }

    // Some private fields by which to reference controls
    Button button = new Button();
    TextBox text = new TextBox();
}

Figure 4  CorrectMultiThreadedForm.cs
using System;
using System.Drawing;
using System.Windows.Forms;
using Microsoft.VisualBasic;

class App{
    // Application entry point
    public static void Main(){
	// Run a Windows Forms message loop
	Application.Run(new CorrectMultiThreadedForm());
    }
}

// A Form-dervied type
class CorrectMultiThreadedForm: Form{
    // Constructor method
    public CorrectMultiThreadedForm(){
	// Create a textbox
	text.Location = new Point(10, 10);
	text.Size = new Size(50, 20);
	Controls.Add(text);
		
	// Create a button
	button.Text = "Beep";
	button.Size = new Size(50, 20);
	button.Location = new Point(80, 10);

	// Regiester Click event handler
	button.Click += new EventHandler(OnClick);

	Controls.Add(button);
		
	// Cache a delegate for repeated reuse
	enableControls = new BooleanCallback(EnableControls);
    }

    // Method called by the button's Click event
    void OnClick(Object sender, EventArgs args){
	// Get an int from a string
	Int32 count = 0;
	try{ count = Int32.Parse(text.Text); } catch(FormatException) {}
		
	// Count to that number
	EnableControls(false);
	WaitCallback async = new WaitCallback(Count);
	ThreadPool.QueueUserWorkItem(async, count);
    }

    // Async method beeps once per second
    void Count(Object param){
	Int32 seconds = (Int32)param;
	for(Int32 index = 0; index < seconds; index++){
	    Interaction.Beep();
	    Thread.Sleep(1000);
        }
        Invoke(enableControls, new Object[]{true});
    }

    void EnableControls(Boolean enable){
	button.Enabled = enable;
	text.Enabled = enable;
    }

    // A delegate type and matching field
    delegate void BooleanCallback(Boolean enable);
    BooleanCallback enableControls;

    // Some private fields by which to reference controls
    Button button = new Button();
    TextBox text = new TextBox();
}