c# - How to execute task in the wpf background while able to provide report and allow cancellation?

Question

I want to execute a long running task after clicking a wpf button. Here what I did.

private void Start(object sender, RoutedEventArgs e)
{
    for (int i = 0; i < 10; i++)
    {
        Thread.Sleep(2000); // simulate task
    }
}

Problem is, this will make wpf gui unresponsive. I also would like to allow cancellation and report progress every 1 second. I expand the code as below.

    DispatcherTimer dispatcherTimer = new DispatcherTimer(); // get progress every second
    private int progress = 0; // for progress reporting
    private bool isCancelled = false; // cancellation

    private void Start(object sender, RoutedEventArgs e)
    {
        InitializeTimer(); // initiallize interval timer 
        Start(10); // execute task
    }

    private void InitializeTimer()
    {
        dispatcherTimer.Tick += dispatcherTimer_Tick;
        dispatcherTimer.Interval = new TimeSpan(0,0,1);
        dispatcherTimer.Start();
    }

    private void dispatcherTimer_Tick(object sender, EventArgs e)
    {
        Logger.Info("Current loop progress " + progress); // report progress
    }

    private void Cancel(object sender, RoutedEventArgs e) // cancel button
    {
        isCancelled = true;
    }

    private int Start(int limit)
    {
        isCancelled = true;
        progress = 0;

        for (int i = 0; i < limit; i++)
        {
            Thread.Sleep(2000); // simulate task
            progress = i; // for progress report
            if (isCancelled) // cancellation
            {
                break;
            }
        }
        return limit;
    }

My target platform is .NET 4.5. What is the recommended way to do this?

Thanks.

Answer 1

I thought I answered your question here. If you need more sample code on how to do this using Task Parallel Library, with CancellationTokenSource and IProgress<T>, here it is:

Action _cancelWork;

private async void StartButton_Click(object sender, RoutedEventArgs e)
{
    this.StartButton.IsEnabled = false;
    this.StopButton.IsEnabled = true;
    try
    {
        var cancellationTokenSource = new CancellationTokenSource();

        this._cancelWork = () => 
        {
            this.StopButton.IsEnabled = false;
            cancellationTokenSource.Cancel();
         };

        var limit = 10;

        var progressReport = new Progress<int>((i) => 
            this.TextBox.Text = (100 * i / (limit-1)).ToString() + "%");

        var token = cancellationTokenSource.Token;

        await Task.Run(() =>
            DoWork(limit, token, progressReport), 
            token);
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
    this.StartButton.IsEnabled = true;
    this.StopButton.IsEnabled = false;
    this._cancelWork = null;
}

private void StopButton_Click(object sender, RoutedEventArgs e)
{
    this._cancelWork?.Invoke();
}

private int DoWork(
    int limit, 
    CancellationToken token,
    IProgress<int> progressReport)
{
    var progress = 0;

    for (int i = 0; i < limit; i++)
    {
        progressReport.Report(progress++);
        Thread.Sleep(2000); // simulate a work item
        token.ThrowIfCancellationRequested();
    }
    return limit;
}