C#中BackgroundWorker组件的用法以及实例

BackgroundWorker组件
功能
在运行程序时，有些操作可能需要很长的执行时间，例如，图像下载、Web服务调用和文件下载、上传等。这些操作可能导致用户界面在操作运行时挂起，如果此时需要用户界面的响应，可以使用BackgroundWorker组件，在不同于应用程序的主用户界面线程的另一线程上异步（“在后台”）执行耗时的操作。图1所示为BackgroundWorker组件。

图1 BackgroundWorker组件
2．属性
BackgroundWorker组件常用属性及说明如表1所示。

表1 BackgroundWorker 组件常用属性及说明
下面详细介绍WorkerSupportsCancellation属性，该属性用于获取或设置一个值，该值指示BackgroundWorker是否支持异步取消。
语法：
public bool WorkerSupportsCancellation { get; set; } 属性值：如果BackgroundWorker支持取消，则为True；否则为False。默认值为False。
示例
WorkerSupportsCancellation属性的使用
本示例主要是使用BackgroundWorker组件的WorkerSupportsCancellation属性，判断是否取消了异步操作。
程序主要代码如下：
if (this.backgroundWorker1.WorkerSupportsCancellation)
{
// The user canceled the operation.
MessageBox.Show("后台操作取消");
} ★★★★★主程序文件完整程序代码★★★★★
using System;
using System.Collections.Generic;
using System.Windows.Forms;
namespace _8_25
{
static class Program
{
///

/// 应用程序的主入口点。
///

[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new frmBackgroundWorker());
}
}
} ★★★★★frmBackgroundWorker窗体设计文件完整程序代码★★★★★
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;
namespace _8_25
{
public partial class frmBackgroundWorker : Form
{
public frmBackgroundWorker()
{
InitializeComponent();
}
private int numberToCompute = 0;
private int highestPercentageReached = 0;
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
e.Result = ComputeFibonacci((int)e.Argument, backgroundWorker1, e);
}
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
this.progressBar1.Value = e.ProgressPercentage;
}
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Error != null)
{
MessageBox.Show(e.Error.Message);
}
else if (e.Cancelled)
{
resultLabel.Text = "Canceled";
}
else
{
resultLabel.Text = e.Result.ToString();
}
this.numericUpDown1.Enabled = true;
startAsyncButton.Enabled = true;
cancelAsyncButton.Enabled = false;
}
private void startAsyncButton_Click(object sender, EventArgs e)
{
resultLabel.Text = String.Empty;
this.numericUpDown1.Enabled = false;
this.startAsyncButton.Enabled = false;
this.cancelAsyncButton.Enabled = true;
numberToCompute = (int)numericUpDown1.Value;
highestPercentageReached = 0;
this.backgroundWorker1.RunWorkerAsync(numberToCompute);
}
private void cancelAsyncButton_Click(object sender, EventArgs e)
{
this.backgroundWorker1.CancelAsync();
this.progressBar1.Value = 0;
this.startAsyncButton.Enabled = true;
this.cancelAsyncButton.Enabled = false;
this.resultLabel.Text = "No Result";
}
long ComputeFibonacci(int n, BackgroundWorker worker, DoWorkEventArgs e)
{
if ((n < 0) || (n > 91))
{
throw new ArgumentException(
"value must be >= 0 and <= 91", "n");
}
long result = 0;
if (worker.CancellationPending)
{
e.Cancel = true;
}
else
{
if (n < 2)
{
result = 1;
}
else
{
result = ComputeFibonacci(n - 1, worker, e) +
ComputeFibonacci(n - 2, worker, e);
}
int percentComplete =
(int)((float)n / (float)numberToCompute * 100);
if (percentComplete > highestPercentageReached)
{
highestPercentageReached = percentComplete;
worker.ReportProgress(percentComplete);
}
}
return result;
}
private void frmBackgroundWorker_Load(object sender, EventArgs e)
{
}
}
} ★★★★★frmBackgroundWorker窗体设计文件完整程序代码★★★★★