ToolStripStatusLabel 没有 InvokeRequired 属性的解决办法
当编写多线程程序时，你希望在线程中修改 Form 窗体上的控件的文本等属性，
但你会得到一个错误：线程间操作无效: 从不是创建控件“xxx”的线程访问它。
引发了“Microsoft.VisualStudio.Debugger.Runtime.CrossThreadMessagingException”类型的异常.
这时有一个解决办法就是使用委托来进行 Invoke 调用，
但是你会发现 ToolStripStatusLabel 没有 InvokeRequired 属性！
这个问题存在的原因是什么呢？
我们看看 Textbox 的继承关系：
public abstract class TextBoxBase : Control
再看看 ToolStripStatusLabel 的继承关系：
public abstract class ToolStripItem : Component, IDropTarget, IComponent, IDisposable再看看 ToolStripStatusLabel 的容器 StatusStrip 的继承关系：
public class ScrollableControl : Control, IComponent, IDisposable我们会发现，这是因为ToolStripItem 是一个组件 Component，而不是一个控件 Control。
解决办法：
方法其实也比较简单，尝试在拥有它们的工具条、状态栏（StatusStrip）上调用扩展方法，并调整委托方法。
实例一：
public class MyForm : System.Windows.Forms.Form {
//UI 元素
private Label lblStatus;
private ProgressBar progressBar1;
//Delegate
private delegate void MyProgressEventsHandler(
object sender, MyProgressEvents e);
private void UpdateUI(object sender, MyProgressEvents e) {
lblStatus.Text = e.Msg;
myProgressControl.Value = e.PercentDone;
}
//ShowProgress 现在可以记录为可从任何线程调用的公共方法。
public void ShowProgress(string msg, int percentDone)
{
if(InvokeRequired)
{
System.EventArgs e = new MyProgressEvents(msg, percentDone);
object[] pList = { this, e };
BeginInvoke(new MyProgressEventsHandler(UpdateUI), pList);
}
else
{
UpdateUI(this, new MyProgressEvents(msg,
PercentDone));
}
}
private void btnStart_Click(object sender, EventArgs e)
{
//启动线程
Thread t = new Thread(new ParameterizedThreadStart(RunsOnWorkerThread));
t.IsBackground = true;
t.Start(input);
}
//线程执行函数
private void RunsOnWorkerThread()
{
int i = 0;
while(...) //loop
{
DoSomethingSlow();
ShowProgress("test",i);
++i;
}
}
}
上面的代码，我们看到什么了？
啥，直接使用 “InvokeRequired”，不用使用“ToolStripStatusLabel.InvokeRequired”这样的格式！
对的，这样就可以了。
当然你也可以使用“StatusStrip.InvokeRequired”这样的形式！
实例二：
上面的例子代码可能不太好理解，我们看看微软官方的例子：
下面的代码示例是一个完整的 Windows 窗体应用程序，它包含一个带有三个按钮和一个文本框的窗体。 第一个按钮演示不安全的跨线程访问，第二个按钮演示使用 Invoke 实现的安全访问，而第三个按钮演示使用 BackgroundWorker 实现的安全访问。
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());
}
}
}
