如何：对 Windows 窗体控件进行线程安全调用
.NET Framework (current version)
发布时间: 2016年5月
如果使用多线程处理来提高 Windows 窗体应用程序的性能，则你必须确保以线程安全的方式调用控件。
访问 Windows 窗体控件不是本身就线程安全的。 如果有两个或两个以上线程操作控件的状态，则可能迫使该控件处于不一致状态。 可能出现其他与线程相关的 bug，例如争用条件和死锁。 请务必确保以线程安全的方式访问控件。
从未使用 Invoke 方法创建控件的线程调用控件是不安全的。 下面是一个非线程安全的调用示例。
// 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. void ThreadProcUnsafe() { this.textBox1.Text = "This text was set unsafely."; }
.NET Framework 可帮助检测你是否以线程安全的方式访问控件。 在调试器中运行应用程序并且未创建控件的线程试图调用控件时，调试器会引发InvalidOperationException 消息，“从并未创建该控件的线程访问该控件 控件名称”。
在调试过程中、在某些情况下以及在运行时均极有可能发生此异常。 当你调试在 .NET Framework 之前用 .NET Framework 2.0 编写的应用程序时可能会看到此异常。 强烈建议你在遇到此问题时修复它，但你可通过将 CheckForIllegalCrossThreadCalls 属性设置为 false 来禁用它。 这使控件可像在 Visual Studio .NET 2003 和 .NET Framework 1.1 下那样运行。
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| 如果你使用的是窗体上的 ActiveX 控件，则在调试器下运行时可能会收到跨线程 InvalidOperationException。 发生此情况时，ActiveX 控件不支持多线程处理。 有关使用 Windows 窗体的 ActiveX 控件的详细信息，请参阅 Windows 窗体和非托管应用程序。 如果你使用的是 Visual Studio，则可通过禁用 Visual Studio 的托管进程来避免此异常，请参阅如何：禁用承载进程。 |
如需对 Windows 窗体控件进行线程安全的调用
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查询控件的 InvokeRequired 属性。
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若 InvokeRequired 返回 true，则用实际调用控件的委托来调用 Invoke。
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若 InvokeRequired 返回 false，则请直接调用控件。
在以下代码示例中，在 ThreadProcSafe 方法中实现了线程安全的调用，该方法由后台线程执行。 若 TextBox 控件的 InvokeRequired 返回true，则 ThreadProcSafe 方法创建一个 SetTextCallback 实例并将其传递到窗体的 Invoke 方法。 这导致在创建了 SetText 控件的线程上调用TextBox 方法，并且在该线程上下文中直接设置 Text 属性。
// Windows Forms control in a thread-safe way. void setTextSafeBtn_Click( this.ThreadProcSafe)); // a thread-safe call on the TextBox control. void ThreadProcSafe() { this.SetText("This text was set safely."); }
VB
' Windows Forms control in a thread-safe way. Private Sub setTextSafeBtn_Click( _ ByVal sender As Object,_ ByVal e As EventArgs) Handles setTextSafeBtn.Click Me.demoThread = New Thread( _ New ThreadStart(AddressOf Me.ThreadProcSafe)) Me.demoThread.Start() End Sub ' This method is executed on the worker thread and makes ' a thread-safe call on the TextBox control. Sub ThreadProcSafe() Me.SetText("This text was set safely.") Sub
C++
// This event handler creates a thread that calls a private: void setTextSafeBtn_Click(Object^ sender,EventArgs^ e) { this->demoThread = gcnew Thread(gcnew ThreadStart(this,&Form1::ThreadProcSafe)); this->demoThread->Start(); } // This method is executed on the worker thread and makes void ThreadProcSafe() { this->SetText("This text was set safely."); }
// the text property on a TextBox control. delegate void SetTextCallback(string text);
' the text property on a TextBox control. Delegate Sub SetTextCallback([text] String)
// 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.
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;
}
}
' calls on a Windows Forms control.
'
' If the calling thread is different from the thread that
' created the TextBox control,sans-serif!important; color:green'>' 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.
Sub SetText(ByVal [text] String)
' 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 Me.textBox1.Invokerequired Then
Dim d New SetTextCallback(AddressOf SetText)
Me.Invoke(d,sans-serif!important; color:blue'>New Object() {[text]})
Else
Me.textBox1.Text = [text]
If
Sub
// calls on a Windows Forms control.
//
// If the calling thread is different from the thread that
// SetTextDelegate and calls itself asynchronously using the
// Invoke method.
// If the calling thread is the same as the thread that created
void SetText(String^ text)
{
// Invokerequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
this->textBox1->Invokerequired)
{
SetTextDelegate^ d =
gcnew SetTextDelegate(this->Invoke(d,sans-serif!important; color:blue'>gcnew array<Object^> { text });
}
else
{
this->textBox1->Text = text;
}
}
通过使用 BackgroundWorker 进行线程安全的调用
在应用程序中实现多线程的首选方式是使用 BackgroundWorker 组件。 BackgroundWorker 组件为多线程处理使用事件驱动模型。 后台线程运行你的 DoWork 事件处理程序，创建了你的控件的线程运行 ProgressChanged 和 RunWorkerCompleted 事件处理程序。 你可以从RunWorkerCompleted 事件处理器中调用控件。
如需通过使用 BackgroundWorker 进行线程安全的调用
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将步骤 1 中创建的方法绑定到 DoWork 实例中的 BackgroundWorker 事件，并将步骤 2 中创建的方法绑定到同一实例的RunWorkerCompleted 事件。
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若要启动后台线程，请调用 RunWorkerAsync 实例的 BackgroundWorker 方法。
在以下代码示例中，DoWork 事件处理程序使用 Sleep 来模拟需要花费一些时间的工作。 它不会调用该窗体的 TextBox 控件。 TextBox 控件的Text 属性直接在 RunWorkerCompleted 事件处理程序中设置。
// preferred way of performing asynchronous operations.
private BackgroundWorker backgroundWorker1;
' preferred way of performing asynchronous operations. WithEvents backgroundWorker1 As BackgroundWorker
private:
BackgroundWorker^ backgroundWorker1;
// BackgroundWorker by calling RunWorkerAsync. // The Text property of the TextBox control is set // when the BackgroundWorker raises the RunWorkerCompleted // event. void setTextBackgroundWorkerBtn_Click( 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. void backgroundWorker1_RunWorkerCompleted( this.textBox1.Text = "This text was set safely by BackgroundWorker."; }
' BackgroundWorker by calling RunWorkerAsync. ' The Text property of the TextBox control is set ' when the BackgroundWorker raises the RunWorkerCompleted ' event. Sub setTextBackgroundWorkerBtn_Click( _ Handles setTextBackgroundWorkerBtn.Click Me.backgroundWorker1.RunWorkerAsync() ' This event handler sets the Text property of the TextBox ' control. It is called on the thread that created the ' TextBox control,sans-serif!important; color:green'>' BackgroundWorker is the preferred way to perform asynchronous ' operations. Sub backgroundWorker1_RunWorkerCompleted( _ As RunWorkerCompletedEventArgs) _ Handles backgroundWorker1.RunWorkerCompleted Me.textBox1.Text = _ "This text was set safely by BackgroundWorker." Sub
// BackgroundWorker by calling RunWorkerAsync.
// The Text property of the TextBox control is set
// when the BackgroundWorker raises the RunWorkerCompleted
void setTextBackgroundWorkerBtn_Click(Object^ sender,sans-serif!important; color:blue'>this->backgroundWorker1->RunWorkerAsync();
}
// This event handler sets the Text property of the TextBox
// control. It is called on the thread that created the
// BackgroundWorker is the preferred way to perform asynchronous
void backgroundWorker1_RunWorkerCompleted(
Object^ sender,RunWorkerCompletedEventArgs^ e)
{
this->textBox1->Text =
"This text was set safely by BackgroundWorker.";
}
也可通过使用 ProgressChanged 事件来报告后台任务的进度。 如需包含该事件的示例，请参阅 BackgroundWorker。
示例
stem; 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. 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 = 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. void setTextUnsafeBtn_Click( this.demoThread = this.ThreadProcUnsafe)); this.demoThread.Start(); } // This method is executed on the worker thread and makes // an unsafe call on the TextBox control. void ThreadProcUnsafe() { "This text was set unsafely."; } // Windows Forms control in a thread-safe way. void setTextSafeBtn_Click( this.ThreadProcSafe)); // a thread-safe call on the TextBox control. void ThreadProcSafe() { "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 // SetTextCallback and calls itself asynchronously using the // Invoke method. // If the calling thread is the same as the thread that created string text) { // Invokerequired required compares the thread ID of the // calling thread to the thread ID of the creating thread. this.textBox1.Invokerequired) { SetTextCallback d = new SetTextCallback(SetText); 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. void setTextBackgroundWorkerBtn_Click( this.backgroundWorker1.RunWorkerAsync(); } // This event handler sets the Text property of the TextBox // control. It is called on the thread that created the // BackgroundWorker is the preferred way to perform asynchronous // operations. void backgroundWorker1_RunWorkerCompleted( this.textBox1.Text = "This text was set safely by BackgroundWorker."; } #region Windows Form Designer generated code void InitializeComponent() { this.textBox1 = new System.Windows.Forms.TextBox(); this.setTextUnsafeBtn = new System.Windows.Forms.Button(); this.setTextSafeBtn = this.setTextBackgroundWorkerBtn = 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,sans-serif!important; color:blue'>this.setTextSafeBtn.Name = "setTextSafeBtn"; this.setTextSafeBtn.TabIndex = 2; this.setTextSafeBtn.Text = "Safe Call"; this.setTextSafeBtn.Click += this.setTextSafeBtn_Click); // setTextBackgroundWorkerBtn this.setTextBackgroundWorkerBtn.Location = new System.Drawing.Point(177,sans-serif!important; color:blue'>this.setTextBackgroundWorkerBtn.Name = "setTextBackgroundWorkerBtn"; this.setTextBackgroundWorkerBtn.TabIndex = 3; this.setTextBackgroundWorkerBtn.Text = "Safe BW Call"; this.setTextBackgroundWorkerBtn.Click += 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.setTextSafeBtn); this.setTextUnsafeBtn); this.textBox1); this.Name = "Form1"; this.Text = this.ResumeLayout(false); this.Performlayout(); } #endregion [STAThread] static void Main() { Application.EnableVisualStyles(); Application.Run(new Form1()); } } }
可靠编程
| 使用任何种类的多线程时，都有可能会遇到非常严重且复杂的 bug。 有关详细信息，请在实现使用多线程处理的任何解决方案之前参阅Managed Threading Best Practices。 |
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运行应用程序并单击“不安全调用”按钮时，你可以立即在文本框中看到“由主线程写入”。 两秒钟之后，尝试进行不安全调用时，Visual Studio 调试器指示发生了异常。 调试器在后台线程中试图直接写入文本框的那一行停止。 你将必须重新启动该应用程序来测试其他两个按钮。 单击“安全调用”按钮时，文本框中显示“由主线程写入”。 两秒钟之后，文本框中被设置为“由后台线程写入 (Invoke)”，表示调用了 Invoke 方法。 单击“安全 BW 调用”按钮时，文本框中显示“由主线程写入”。 两秒钟之后，文本框被设置为“在后台线程完成后由主线程写入”，表示调用了RunWorkerCompleted 的 BackgroundWorker 事件的处理程序。