C#,背景工作者

Question

我有一个使用该BackgroundWorker组件的示例WinForms应用程序.它工作正常,但当我按下Cancel按钮取消后台线程时,它不会取消线程.当我按下Cancel按钮来调用.CancelAsync()方法时,在RunWorkerCompleted事件处理程序中,e.Cancelled属性始终保持不变false.我想当我按下Cancel按钮时应该设置为true.

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    for (int i = 1; i <= 100; i++)
    {
       // Wait 100 milliseconds.
       Thread.Sleep(100);
       // Report progress.
       if (backgroundWorker1.CancellationPending == true)
       {
           //label1.Text = "Cancelled by user.";
           break;
        }

        backgroundWorker1.ReportProgress(i);
     }
}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    // Change the value of the ProgressBar to the BackgroundWorker progress.
    progressBar1.Value = e.ProgressPercentage;
    // Set the text.
    label1.Text = e.ProgressPercentage.ToString();
}

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    if (e.Cancelled == true)
    {
        label1.Text = "Canceled!";
    }
    else if (e.Error != null)
    {
        label1.Text = "Error: " + e.Error.Message;
    }
    else
    {
         label1.Text = "Done!";
    }
}

private void button2_Click(object sender, EventArgs e)
{
    if (backgroundWorker1.WorkerSupportsCancellation == true)
    {
        // Cancel the asynchronous operation.
        backgroundWorker1.CancelAsync();
    }
}

Answer 1

Canceled属性仍然是false,因为您突破循环,然后允许backgroundworker的DoWork函数以正常方式结束.您永远不会告诉您的后台工作组件实际上已接受待处理的取消.

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    for (int i = 1; i <= 100; i++)
    {
        // Wait 100 milliseconds.
        Thread.Sleep(100);

        if (backgroundWorker1.CancellationPending)
        {
            e.Cancel = true;
            break;
        }

        // Report progress.
        backgroundWorker1.ReportProgress(i);
    }
}

区别很重要,因为有时您可能需要在检测到CancellationPending请求时已经完成的回滚工作,因此在您实际完成取消之前可能需要一段时间.