Question

我在WPF应用程序中有一个BackgroundWorker。如果条件为真，我想立即停止处理_DoWork方法并直接转到_RunWorkerCompleted。我正在使用.CancelAsync，但此后的代码继续执行。

如何取消_DoWork并进入_RunWorkerCompleted？

示例：

private BackgroundWorker step1 = new BackgroundWorker();

public MyWindow()
{
    InitializeComponent();
    step1.WorkerSupportsCancellation = true;
    step1.DoWork += new DoWorkEventHandler(step1_DoWork);
    step1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(step1_RunWorkerCompleted);
}

private void step1_DoWork(object sender, DoWorkEventArgs e)
{
    if (someCondition)
    {
        step1.CancelAsync();                
    }
    // code I do not want to execute
}

private void step1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    // I want to jump here from the cancel point
}

Answer 1

CancelAsync是一种方法，旨在由除DoWork处理程序之外的调用，以指示DoWork处理程序应该停止执行。 DoWork处理程序应该检查BGW是否请求取消，如果是，则停止执行（通过返回，抛出异常或者不执行进一步的工作）。

Answer 2

在DoWork处理程序中，检查取消状态。

private void step1_DoWork(object sender, DoWorkEventArgs e)
{
    if (someCondition)
    {
        step1.CancelAsync();                
    }

    if (!step1.CancellationPending)
    {
        // code I do not want to execute
    }
    else
    {
        e.Cancel = true;
        return;
    }
}

Answer 3

    private void startAsyncButton_Click(object sender, EventArgs e)
    {
        if (backgroundWorker1.IsBusy != true)
        {
            // Start the asynchronous operation.
            backgroundWorker1.RunWorkerAsync();
        }
    }

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

    // This event handler is where the time-consuming work is done.
    private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
        BackgroundWorker worker = sender as BackgroundWorker;

        for (int i = 1; i <= 10; i++)
        {
            if (worker.CancellationPending == true)
            {
                e.Cancel = true;
                break;
            }
            else
            {
                // Perform a time consuming operation and report progress.
                System.Threading.Thread.Sleep(500);
                worker.ReportProgress(i * 10);
            }
        }
    }

    // This event handler updates the progress.
    private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        resultLabel.Text = (e.ProgressPercentage.ToString() + "%");
    }

    // This event handler deals with the results of the background operation.
    private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        if (e.Cancelled == true)
        {
            resultLabel.Text = "Canceled!";
        }
        else if (e.Error != null)
        {
            resultLabel.Text = "Error: " + e.Error.Message;
        }
        else
        {
            resultLabel.Text = "Done!";
        }
    }
}

}

取消DoWork并进入RunWorkerCompleted

3 个答案: