Comment réinitialiser un CancellationToken correctement?

Question

je joue avec le tour async ctp ce matin et ont un programme simple avec un button et un label. Cliquez sur le button et il commence à mettre le label, arrêtez le button il cesse d'écrire à la label. Cependant, je ne suis pas sûr de savoir comment réinitialiser le CancellationTokenSource afin que je puisse relancer le processus. Mon code est ci-dessous:

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

You need to recreate the CancellationTokenSource - there is no way to "reset" this once you set it.

This could be as simple as:

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

Even I had same problem and I figured it out that, best way to solve it is to create cancellation token source newly just before calling the method.

this is what I do on my start button click:

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

I change the caption for the same button to cancel and when a click occurs on cancel, i call

cancellationTokenSource.Cancel();

Here is the full code:

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);
            }
        }