Async/Await with a WinForms ProgressBar

Question

I\'ve gotten this type of thing working in the past with a BackgroundWorker, but I want to use the new async/await approach of .NET 4.5. I may be barking up the wrong tree.

Answer 1

private async void button1_Click(object sender, EventArgs e)
{
    IProgress<int> progress = new Progress<int>(value => { progressBar1.Value = value; });
    await Task.Run(() =>
    {
        for (int i = 0; i <= 100; i++)
            progress.Report(i);
    });
}

Correct me if I'm wrong, but this seems to be the easiest way to update a progress bar.

Answer 2

@StephenCleary's answer is correct. Though, I had to make a little modification to his answer to get the behavior what I think OP wants.

public void GoAsync() //no longer async as it blocks on Appication.Run
{
    var owner = new Win32Window(Process.GetCurrentProcess().MainWindowHandle);
    _progressForm = new Form1();

    var progress = new Progress<int>(value => _progressForm.UpdateProgress(value));

    _progressForm.Activated += async (sender, args) =>
        {
            await Go(progress);
            _progressForm.Close();
        };

    Application.Run(_progressForm);
}

Answer 3

The async and await keywords do not mean "run on a background thread." I have an async/await intro on my blog that describes what they do mean. You must explicitly place CPU-bound operations on a background thread, e.g., Task.Run.

Also, the Task-based Asynchronous Pattern documentation describes the common approaches with async code, e.g., progress reporting.

class Manager
{
  private static Form1 _progressForm;

  public async Task GoAsync()
  {
    var owner = new Win32Window(Process.GetCurrentProcess().MainWindowHandle);
    _progressForm = new Form1();
    _progressForm.Show(owner);

    var progress = new Progress<int>(value => _progressForm.UpdateProgress(value));
    await Go(progress);

    _progressForm.Hide();
  }

  private Task<bool> Go(IProgress<int> progress)
  {
    return Task.Run(() =>
    {
      var job = new LongJob();
      job.Spin(progress);
      return true;
    });
  }
}

class LongJob
{
  public void Spin(IProgress<int> progress)
  {
    for (var i = 1; i <= 100; i++)
    {
      Thread.Sleep(25);
      if (progress != null)
      {
        progress.Report(i);
      }
    }
  }
}

Note that the Progress<T> type properly handles thread marshaling, so there's no need for marshaling within Form1.UpdateProgress.