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#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());
        }
        
    }
}

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.