如何正确重置CancellationToken？

Question

async ctp今天早上我一直在玩,并有一个简单的程序与a button和a label.点击button它开始更新label,停止button它停止写入label.但是,我不确定如何重置,CancellationTokenSource以便我可以重新启动该过程.我的代码如下:

public partial class MainWindow : Window
{
    CancellationTokenSource cts = new CancellationTokenSource();
    public MainWindow()
    {
        InitializeComponent();
        button.Content = "Start";
    }

    async Task DoWork(CancellationToken cancelToken)
    {
        int i = 0;
        while (!cancelToken.IsCancellationRequested)
        {
            label.Content = i++.ToString();
            await TaskEx.Delay(50, cancelToken);
        }
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        if (button.Content == "Start")
        {
            button.Content = "Stop";
            DoWork(cts.Token);
        }
        else
        {
            button.Content = "Start";
            cts.Cancel();
        }
    }
}

Answer 1

你需要重新创建CancellationTokenSource- 一旦你设置它就无法"重置"它.

这可能很简单:

private void Button_Click(object sender, RoutedEventArgs e)
{
    if (button.Content == "Start")
    {
        button.Content = "Stop";
        cts.Dispose(); // Clean up old token source....
        cts = new CancellationTokenSource(); // "Reset" the cancellation token source...
        DoWork(cts.Token);
    }
    else
    {
        button.Content = "Start";
        cts.Cancel();
    }
}

Answer 2

即使我有同样的问题,我也知道,解决它的最佳方法是在调用方法之前新创建取消令牌源.

这是我在开始按钮点击时所做的事情:

cancellationTokenSource = new CancellationTokenSource();
cancellationToken = cancellationTokenSource.Token;
Task.Factory.StartNew(StartUpload, cancellationToken);

我改变相同按钮的标题取消,当取消时发生点击,我打电话

cancellationTokenSource.Cancel();

这是完整的代码:

if (button3.Text != "&Start Upload")
        {
            cancellationTokenSource.Cancel();
        }
        else
        {
            try
            {
                cancellationTokenSource = new CancellationTokenSource();
                cancellationToken = cancellationTokenSource.Token;
                Task.Factory.StartNew(StartUpload, cancellationToken);
            }
            catch (AggregateException ex)
            {
                var builder = new StringBuilder();
                foreach (var v in ex.InnerExceptions)
                    builder.Append("\r\n" + v.InnerException);
                MessageBox.Show("There was an exception:\r\n" + builder.ToString());
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

Answer 3

现在，在 .NET 6 中，您可以使用查看此问题TryReset()的方法和CancellationTokenSource.cs了解更多详细信息。Attempts to reset the CancellationTokenSource to be used for an unrelated operation.