C# BackgroundWorker 的使用方法

可参见:    http://msdn.microsoft.com/zh-cn/library/system.componentmodel.backgroundworker(VS.80).aspx

      BackgroundWorker 类允许您在单独的专用线程上运行操作。耗时的操作（如下载和数据库事务）在长时间运行时可能会导致用户界面 (UI) 似乎处于停止响应状态。如果您需要能进行响应的用户界面，而且面临与这类操作相关的长时间延迟，则可以使用 BackgroundWorker 类方便地解决问题。

      若要在后台执行耗时的操作，请创建一个 BackgroundWorker，侦听那些报告操作进度并在操作完成时发出信号的事件。可以通过编程方式创建 BackgroundWorker，也可以将它从“工具箱”的“组件”选项卡中拖到窗体上。如果在 Windows 窗体设计器中创建 BackgroundWorker，则它会出现在组件栏中，而且它的属性会显示在“属性”窗口中。

      若要设置后台操作，请为 DoWork 事件添加一个事件处理程序。在此事件处理程序中调用耗时的操作。若要启动该操作，请调用 RunWorkerAsync。若要收到进度更新通知，请对 ProgressChanged 事件进行处理。若要在操作完成时收到通知，请对 RunWorkerCompleted 事件进行处理。

下面代码演示如何用BackgroundWorker计算斐波那契数列并表示当前进度

/Form1.cs/// using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms; namespace WindowsApplication2 { public partial class Form1 : Form { private int numberToCompute = 0; private int highestPercentageReached = 0; public Form1() { InitializeComponent(); InitializeBackgoundWorker(); } // Set up the BackgroundWorker object by // attaching event handlers. private void InitializeBackgoundWorker() { backgroundWorker1.DoWork += new DoWorkEventHandler(backgroundWorker1_DoWork); backgroundWorker1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(backgroundWorker1_RunWorkerCompleted); backgroundWorker1.ProgressChanged += new ProgressChangedEventHandler(backgroundWorker1_ProgressChanged); } private void startAsyncButton_Click(System.Object sender, System.EventArgs e) { // Reset the text in the result label. resultLabel.Text = String.Empty; // Disable the UpDown control until // the asynchronous operation is done. this.numericUpDown1.Enabled = false; // Disable the Start button until // the asynchronous operation is done. this.startAsyncButton.Enabled = false; // Enable the Cancel button while // the asynchronous operation runs. this.cancelAsyncButton.Enabled = true; // Get the value from the UpDown control. numberToCompute = (int)numericUpDown1.Value; // Reset the variable for percentage tracking. highestPercentageReached = 0; // Start the asynchronous operation. backgroundWorker1.RunWorkerAsync(numberToCompute); } private void cancelAsyncButton_Click(System.Object sender, System.EventArgs e) { // Cancel the asynchronous operation. this.backgroundWorker1.CancelAsync(); // Disable the Cancel button. cancelAsyncButton.Enabled = false; } // This event handler is where the actual, // potentially time-consuming work is done. private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e) { // Get the BackgroundWorker that raised this event. BackgroundWorker worker = sender as BackgroundWorker; // Assign the result of the computation // to the Result property of the DoWorkEventArgs // object. This is will be available to the // RunWorkerCompleted eventhandler. e.Result = ComputeFibonacci((int)e.Argument, worker, e); } // This event handler deals with the results of the // background operation. private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { // First, handle the case where an exception was thrown. if (e.Error != null) { MessageBox.Show(e.Error.Message); } else if (e.Cancelled) { // Next, handle the case where the user canceled // the operation. // Note that due to a race condition in // the DoWork event handler, the Cancelled // flag may not have been set, even though // CancelAsync was called. resultLabel.Text = "Canceled"; } else { // Finally, handle the case where the operation // succeeded. resultLabel.Text = e.Result.ToString(); } // Enable the UpDown control. this.numericUpDown1.Enabled = true; // Enable the Start button. startAsyncButton.Enabled = true; // Disable the Cancel button. cancelAsyncButton.Enabled = false; } // This event handler updates the progress bar. private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e) { this.progressBar1.Value = e.ProgressPercentage; } // This is the method that does the actual work. For this // example, it computes a Fibonacci number and // reports progress as it does its work. long ComputeFibonacci(int n, BackgroundWorker worker, DoWorkEventArgs e) { // The parameter n must be >= 0 and <= 91. // Fib(n), with n > 91, overflows a long. if ((n < 0) || (n > 91)) { throw new ArgumentException("value must be >= 0 and <= 91", "n"); } long result = 0; // Abort the operation if the user has canceled. // Note that a call to CancelAsync may have set // CancellationPending to true just after the // last invocation of this method exits, so this // code will not have the opportunity to set the // DoWorkEventArgs.Cancel flag to true. This means // that RunWorkerCompletedEventArgs.Cancelled will // not be set to true in your RunWorkerCompleted // event handler. This is a race condition. if (worker.CancellationPending) { e.Cancel = true; } else { if (n < 2) { result = 1; } else { result = ComputeFibonacci(n - 1, worker, e) + ComputeFibonacci(n - 2, worker, e); } // Report progress as a percentage of the total task. int percentComplete = (int)((float)n / (float)numberToCompute * 100); if (percentComplete > highestPercentageReached) { highestPercentageReached = percentComplete; worker.ReportProgress(percentComplete); } } return result; } } }