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;
}
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