c# - Async Progress Bar Update

Question

I am trying to use an async await to update a progress bar on my WinForm based on a copy operation, but the progress bar will only update when the Copy function has finished, and then throws an exception that it can't update as it's not on the same thread?

The Copy function doesn't need to interact with the UI but the Progress function does.

The UI isn't blocked though, so it would appear the async part is working as expected, it's just interacting with the UI thread that isn't.

long fileProgress = 0;
long totalProgress = 0;
bool complete = false;

CopyFileEx.CopyFileCallbackAction callback(FileInfo source, FileInfo destination, object state, long totalFileSize, long totalBytesTransferred)
{
      fileProgress = totalBytesTransferred;
      totalProgress = totalFileSize;
      return CopyFileEx.CopyFileCallbackAction.Continue;
}

async Task Progress()
{
      await Task.Run(() =>
      {
           while (!complete)
           {
                if (fileProgress != 0 && totalProgress != 0)
                {
                     fileProgressBar.Value = (int)(fileProgress / totalProgress) * 100;
                }
           }
      });
}

private async void startButton_Click(object sender, EventArgs e)
{
      Copy();
      await Progress();
      MessageBox.Show("Done");
}

void Copy()
{
      Task.Run(() =>
      {
           CopyFileEx.FileRoutines.CopyFile(new FileInfo(@"C:\_USBFear.rar"), new FileInfo(@"H:Fear.rar"), CopyFileEx.CopyFileOptions.All, callback, null);
           complete = true;
      });
}

Answer 1

You need to use IProgress<T> here :

private async void startButton_Click(object sender, EventArgs e)
{
      var progress = new Progress<int>(percent =>
      {
         fileProgressBar.Value = percent;
      });

      await Copy(progress);

      MessageBox.Show("Done");
}

void Copy(IProgress<int> progress)
{
      Task.Run(() =>
      {
           CopyFileEx.FileRoutines.CopyFile(new FileInfo(@"C:\_USBFear.rar"), new FileInfo(@"H:Fear.rar"), CopyFileEx.CopyFileOptions.All, callback, null,progress);
           complete = true;
      });
}

and your callback method can report the progress of IProgress<T> like:

CopyFileEx.CopyFileCallbackAction callback(FileInfo source, FileInfo destination, object state, long totalFileSize, long totalBytesTransferred,IProgress<int> progress)
{
      fileProgress = totalBytesTransferred;
      totalProgress = totalFileSize;
      progress.Report(Convert.ToInt32(fileProgress/totalProgress));
      return CopyFileEx.CopyFileCallbackAction.Continue;
}

You can look at this very good article by Stephen Cleary