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2010-05-12 16:53:04


使用多线程提高 Windows 窗体应用程序的性能时,必须注意以线程安全方式调用控件。


示例

访问 Windows 窗体控件本质上不是线程安全的。如果有两个或多个线程操作某一控件的状态,则可能会迫使该控件进入一种不一致的状态。还可能出现其他与线程相关的 bug,包括争用情况和死锁。确保以线程安全方式访问控件非常重要。


.NET Framework 有助于在以非线程安全方式访问控件时检测到这一问题。在调试器中运行应用程序时,如果创建某控件的线程之外的其他线程试图调用该控件,则调试器会引发一个 InvalidOperationException,并显示以下消息:“从不是创建控件控件名称 的线程访问它。”


此异常在调试期间和运行时的某些情况下可靠地发生。强烈建议您在显示此错误信息时修复此问题。在调试以 .NET Framework 2.0 版之前的 .NET Framework 编写的应用程序时,可能会出现此异常。


说明:

可以通过将 CheckForIllegalCrossThreadCalls 属性的值设置为 false 来禁用此异常。这会使控件以与在 Visual Studio 2003 下相同的方式运行。



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());
        }

    }
}


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