C# async/await Progress event on Task<> object

Question

I\'m completely new to C# 5\'s new async/await keywords and I\'m interested in the best way to implement a progress event.

Now I\'d prefer

Answer 1

I had to piece together this answer from several posts as I was trying to figure out how to make this work for code that is less trivial (ie events notify changes).

Let's assume you have a synchronous item processor that will announce the item number it is about to start work on. For my example I am just going to manipulate the content of the Process button, but you can easily update a progress bar etc.

private async void BtnProcess_Click(object sender, RoutedEventArgs e)
{       
    BtnProcess.IsEnabled = false; //prevent successive clicks
    var p = new Progress();
    p.ProgressChanged += (senderOfProgressChanged, nextItem) => 
                    { BtnProcess.Content = "Processing page " + nextItem; };

    var result = await Task.Run(() =>
    {
        var processor = new SynchronousProcessor();

        processor.ItemProcessed += (senderOfItemProcessed , e1) => 
                                ((IProgress) p).Report(e1.NextItem);

        var done = processor.WorkItWorkItRealGood();

        return done ;
    });

    BtnProcess.IsEnabled = true;
    BtnProcess.Content = "Process";
}

The key part to this is closing over the Progress<> variable inside ItemProcessed subscription. This allows everything to Just works ™.