C#跨线程调用窗体控件（比如TextBox）引发的线程安全问题_.NET_编程开发_程序员俱乐部

如何：对 Windows 窗体控件进行线程安全调用

class="sentence SentenceHover" data-source="Access to Windows Forms controls is not inherently thread safe." data-guid="cefa7256b29da0916b1cd034799db43f">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。 还可能会出现其他与线程相关的 Bug，例如争用情况和死锁。 确保以线程安全方式访问控件非常重要。

created the control without using the <span class="mtpsTagOuterHtml" >Invoke method." data-guid="722aea9df3a444de1acbd9bb89d58249">在未使用 Invoke 方法的情况下，从不是创建某个控件的线程的其他线程调用该控件是不安全的。 以下非线程安全的调用的示例。

        // 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.";
        }

Framework helps you detect when you are accessing your controls in a manner that is not thread safe." data-guid="af025aed231c6a72206e616fdfcb107b">.NET Framework 可帮助您检测以非线程安全方式访问控件这一问题。 debugger, and a thread other than the one which created a control tries to call that control, the debugger raises an <span class="mtpsTagOuterHtml" >InvalidOperationException with the message, "Control <span class="parameter">control name accessed from a thread other than the thread it was created on."" data-guid="65b04c7d12ecae567f6f7fdf91b9a001">在调试器中运行应用程序时，如果一个不是创建某个控件的线程的其他线程调用该控件，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。 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。 can disable it by setting the <span class="mtpsTagOuterHtml" >CheckForIllegalCrossThreadCalls property to <span class="input">false." data-guid="1c4ff81dae19933648c8ef80682c7d61">我们强烈建议您在发现此问题时进行修复，但您可以通过将 CheckForIllegalCrossThreadCalls 属性设置为 false 来禁用它。（不推荐）

对 Windows 窗体控件进行线程安全调用

1. 查询控件的 InvokeRequired 属性。

2. 如果 InvokeRequired 返回 true，则使用实际调用控件的委托来调用 Invoke。

3. 如果 InvokeRequired 返回 false，则直接调用控件。

　　在下面的代码示例中，将在由后台线程执行的 ThreadProcSafe 方法中实现线程安全调用。 instance of <span class="code">SetTextCallback and passes that to the form's <span class="mtpsTagOuterHtml" >Invoke method." data-guid="b4a05c0a9cd605de7fe0298c7caedff6">如果 TextBox 控件的 InvokeRequired 返回 true，则 ThreadProcSafe 方法会创建 SetTextCallback 的一个实例，并将该实例传递给窗体的 Invoke 方法。 这使得 SetText 方法被创建 TextBox 控件的线程调用，而且在此线程上下文中将直接设置 Text 属性。

       // 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.");
        }

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());
        }

    }
}