BackgroundWorker 类

今天在msdn上无意中看到一个控件（以前没有注意到过）BackgroundWorker ，建立winform工程后，可以在工具栏看到这个控件

http://msdn.microsoft.com/zh-cn/library/system.componentmodel.backgroundworker%28v=VS.80%29.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。 

如果后台操作需要参数，请在调用 RunWorkerAsync 时给出参数。在 DoWork 事件处理程序内部，可以从 DoWorkEventArgs.Argument 属性中提取该参数

 

下面的代码示例演示如何使用 BackgroundWorker 类异步执行耗时的操作。该操作计算选定的斐波纳契数，在计算过程中报告进度更新，并允许取消挂起的计算。

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());        }    }}