TaskCanceledException when calling Task.Delay with a CancellationToken in an keyboard event

Question

I am trying to delay the processing of a method (SubmitQuery() in the example) called from an keyboard event in WinRT until there has been no further events for a time period (500ms in this case).

I only want SubmitQuery() to run when I think the user has finished typing.

Using the code below, I keep getting a System.Threading.Tasks.TaskCanceledException when Task.Delay(500, cancellationToken.Token); is called. What am I doing wrong here please?

CancellationTokenSource cancellationToken = new CancellationTokenSource();

private async void SearchBox_QueryChanged(SearchBox sender, SearchBoxQueryChangedEventArgs args)
{

        cancellationToken.Cancel();
        cancellationToken = new CancellationTokenSource();

    await Task.Delay(500, cancellationToken.Token);

    if (!cancellationToken.IsCancellationRequested)
    {
        await ViewModel.SubmitQuery();
    }
}

Answer 1

That's to be expected. When you cancel the old Delay, it will raise an exception; that's how cancellation works. You can put a simple try/catch around the Delay to catch the expected exception.

Note that if you want to do time-based logic like this, Rx is a more natural fit than async.