C#，后台 worker

Question

我有一个使用 BackgroundWorker 组件的示例 WinForms 应用程序。它工作正常，但是当我点击 Cancel 按钮取消后台线程时，它并没有取消线程。当我点击 Cancel 按钮调用 .CancelAsync() 方法时，然后在 RunWorkerCompleted 事件处理程序中 e.Cancelled属性始终保持 false。我想当我点击 Cancel 按钮时，它应该设置为 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 属性仍然为 false，因为您跳出循环，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人员组件实际接受了挂起的取消。

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，因为有时您可能希望在检测到 CancellationPending 请求时回滚已经完成的工作，因此可能需要一段时间才能真正完成取消。