实现使用后台操作的窗体

如果有一个需要很长时间才能完成的操作，而且不希望用户界面中出现延迟，则可以使用 BackgroundWorker 类来在另一个线程上运行该操作。 

 

创建了一个计算 Fibonacci 数的窗体。该计算运行于用户界面线程之外的另一个线程上，因此用户界面可在计算进行的同时继续运行，而不会出现延迟

 

 

在应用程序中实现多线程的首选方式是使用 BackgroundWorker 组件。BackgroundWorker 组件使用事件驱动模型实现多线程。辅助线程运行 DoWork 事件处理程序，创建控件的线程运行 ProgressChanged 和 RunWorkerCompleted 事件处理程序。注意不要从 DoWork 事件处理程序调用您的任何控件。

下面的代码示例不异步执行任何工作，因此没有 DoWork 事件处理程序的实现。TextBox 控件的 Text 属性在 RunWorkerCompleted 事件处理程序中直接设置

 

 

using System;using System.Collections;using System.ComponentModel;using System.Drawing;using System.Threading;using System.Windows.Forms;namespace BackgroundWorkerExample{ public class FibonacciForm : System.Windows.Forms.Form { private int numberToCompute = 0; private int highestPercentageReached = 0; private System.Windows.Forms.NumericUpDown numericUpDown1; private System.Windows.Forms.Button startAsyncButton; private System.Windows.Forms.Button cancelAsyncButton; private System.Windows.Forms.ProgressBar progressBar1; private System.Windows.Forms.Label resultLabel; private System.ComponentModel.BackgroundWorker backgroundWorker1; public FibonacciForm() { 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; } #region Windows Form Designer generated code private void InitializeComponent() { this.numericUpDown1 = new System.Windows.Forms.NumericUpDown(); this.startAsyncButton = new System.Windows.Forms.Button(); this.cancelAsyncButton = new System.Windows.Forms.Button(); this.resultLabel = new System.Windows.Forms.Label(); this.progressBar1 = new System.Windows.Forms.ProgressBar(); this.backgroundWorker1 = new System.ComponentModel.BackgroundWorker(); ((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).BeginInit(); this.SuspendLayout(); // // numericUpDown1 // this.numericUpDown1.Location = new System.Drawing.Point(16, 16); this.numericUpDown1.Maximum = new System.Decimal(new int[] { 91, 0, 0, 0}); this.numericUpDown1.Minimum = new System.Decimal(new int[] { 1, 0, 0, 0}); this.numericUpDown1.Name = "numericUpDown1"; this.numericUpDown1.Size = new System.Drawing.Size(80, 20); this.numericUpDown1.TabIndex = 0; this.numericUpDown1.Value = new System.Decimal(new int[] { 1, 0, 0, 0}); // // startAsyncButton // this.startAsyncButton.Location = new System.Drawing.Point(16, 72); this.startAsyncButton.Name = "startAsyncButton"; this.startAsyncButton.Size = new System.Drawing.Size(120, 23); this.startAsyncButton.TabIndex = 1; this.startAsyncButton.Text = "Start Async"; this.startAsyncButton.Click += new System.EventHandler(this.startAsyncButton_Click); // // cancelAsyncButton // this.cancelAsyncButton.Enabled = false; this.cancelAsyncButton.Location = new System.Drawing.Point(153, 72); this.cancelAsyncButton.Name = "cancelAsyncButton"; this.cancelAsyncButton.Size = new System.Drawing.Size(119, 23); this.cancelAsyncButton.TabIndex = 2; this.cancelAsyncButton.Text = "Cancel Async"; this.cancelAsyncButton.Click += new System.EventHandler(this.cancelAsyncButton_Click); // // resultLabel // this.resultLabel.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D; this.resultLabel.Location = new System.Drawing.Point(112, 16); this.resultLabel.Name = "resultLabel"; this.resultLabel.Size = new System.Drawing.Size(160, 23); this.resultLabel.TabIndex = 3; this.resultLabel.Text = "(no result)"; this.resultLabel.TextAlign = System.Drawing.ContentAlignment.MiddleCenter; // // progressBar1 // this.progressBar1.Location = new System.Drawing.Point(18, 48); this.progressBar1.Name = "progressBar1"; this.progressBar1.Size = new System.Drawing.Size(256, 8); this.progressBar1.Step = 2; this.progressBar1.TabIndex = 4; // // backgroundWorker1 // this.backgroundWorker1.WorkerReportsProgress = true; this.backgroundWorker1.WorkerSupportsCancellation = true; // // FibonacciForm // this.ClientSize = new System.Drawing.Size(292, 118); this.Controls.Add(this.progressBar1); this.Controls.Add(this.resultLabel); this.Controls.Add(this.cancelAsyncButton); this.Controls.Add(this.startAsyncButton); this.Controls.Add(this.numericUpDown1); this.Name = "FibonacciForm"; this.Text = "Fibonacci Calculator"; ((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).EndInit(); this.ResumeLayout(false); } #endregion [STAThread] static void Main() { Application.Run(new FibonacciForm()); } }}

 

 

CSC编译一下