新手老问题跨线程的控件访问

新手老问题---------跨线程的控件访问

电子科技大学03级02班周银辉

新手经常会遇到这样的问题: a线程去访问b线程的控件,编译器报错(.net1.0编译时好像不会报,.net2.0是肯定会的).

解决方法有3种:
1, 不安全的方法: 将 Control.CheckForIllegalCrossThreadCalls 设置为false (.net1.0中没有)
2,安全的方法:　异步委托
3, 安全的方法: 就是使用BackgroundWorker来替代你自己创建的线程(.net1.0中没有)

以下是示例代码

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.";

}

Windows Form Designer generated code

[STAThread]

static void Main()

{

Application.EnableVisualStyles();

Application.Run(new Form1());

}

在使用方法2时的注意事项: 不要将除了控件访问外其他逻辑代码放到委托的回调方法中.