有关Backgroundworker

（一）Backgroundworker取消时应该用的有关代码：

CancelAsync方法是在前台主线程用的，CancellationPending属性是在后台子线程用的。实际的使用方式应该是这样的：

1.要取消异步操作，一般来说是在窗体中点击“取消”按钮，在“取消”按钮的单击事件中触发CancelAsync方法

private void btn_Stop_Click(object sender, EventArgs e)

{

backgroundWorker1.CancelAsync(); //提交取消命令,但还未取消

}

2.这时，CancellationPending由false变为true

3.再在DoWork事件里获取CancellationPending，依据它来处理后台任务，比如说直接return;

static void bw_DoWork(object sender, DoWorkEventArgs e) 
{

//判断是否取消操作 
if (bw.CancellationPending) 
{ 
e.Cancel = true; //这里才真正取消 
return; 
}

}

4.最后完成时判断

static void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)

{

if (e.Cancelled)

Console.WriteLine("You cancelled!");

else if (e.Error != null)

Console.WriteLine("Worker exception: " + e.Error.ToString());

else

{

Console.WriteLine("Complete - " + e.Result); // 从DoWork

}

}

（二）Backgroundworker相关代码：

一．开始

BackgroundWorker backgroundWorker1 = new BackgroundWorker();

//在另一个线程里开始操作（btnStart是一个按钮控件）

//也可以利用RunWokerAsync()方法传递参数，

private void btnStart_Click(object sender, EventArgs e)

{

backgroundWorker1.RunWokerAsync(2000/*参数是可选的*/);

}

//DoWork事件在另一个线程里执行

private void backgroundWorker1_DoWork(objectsender,DoWorkeventArgs e)

{

//允许长时间的操作

int input = (int)e.Argument;

Thread.Sleep(input);

}

二．显示后台操作进度

BackgroundWorker backgroundWorker1 = new BackgroundWorker();

backgroundWorker1.WorkerReportsProgress = true;

private void btnStart_Click(object sender, EventArgs e)

{

backgroundWorker1.RunWokerAsync();

}

private void backgroundWorker1_DoWork(object sender, DoWorkeventArgs e)

{

for (int i = 1; i < 11; i++)

{

Thread.Sleep(2000);

backgroundWorker1.ReportProgress(i*10);

}

}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)

{

//progressBar1是ProgressBar控件

progressBar1.Value = e.ProgressPercentage;

}

三．取消后台操作

BackgroundWorker backgroundWorker1 = new BackgroundWorker();

backgroundWorker1.WorkerReportsProgress = true;

backgroundWorker1.WorkerSupportsCancellation = true;

private void btnStart_Click(object sender, EventArgs e)

{

backgroundWorker1.RunWokerAsync();

}

private void btnCancel_Click(object sender, EventArgs e)

{

backgroundWorker1.CancelAsync();

}

private void backgroundWorker1_DoWork(object sender, DoWorkeventArgs e)

{

for (int i = 1; i < 11; i++)

{

Thread.Sleep(2000);

backgroundWorker1.ReportProgress(i*10);

if(backgroundWorker1.CancellationPending)

{

e.Cancel = true;

return;

}

}

}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)

{

progressBar1.Value = e.ProgressPercentage;

}

四．后台操作完成后，反馈给用户

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)

{

if(e.Cancelled)

{

MessageBox.Show("Operation Cancelled");

}

else

{

MessageBox.Show("OperationCompleted");

}

}

五．从后台操作返回值

private void backgroundWorker1_DoWork(object sender, DoWorkeventArgs e)

{

Thread.Sleep(2000);

//在此处设置返回值

e.Result = 10;

}

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)

{

//在此处接收传递回来的值

intreturnValue = (int)e.Result;

}