Async callback to awaitable Task<> z

http://blog.tedd.no/2013/09/13/async-callback-to-awaitable-task/

 

The Async-Await feature in .Net is really super. At least until it comes to debugging, exception handling and race conditions. In short it cuts down on code, bugs, complexity and allows for linear programming. Traditional async programming uses callbacks (events) that adds to code complexity, it also forces an unnatural break in your code.

Luckily more and more .Net-objects is getting support for async-await, and the most important ones are already implemented.

However, there is also a very easy way to convert a traditional async into async-await. In the sample code below I have made an awaitable task out of the camera for WP7, but this can be applied to any async callback.

public static Task<PhotoResult> TakePicture()

{

    var taskCompletionSource = new TaskCompletionSource<PhotoResult>();

    var cameraCaptureTask = new CameraCaptureTask();

    cameraCaptureTask.Completed += (sender, result) => taskCompletionSource.SetResult(result);

    cameraCaptureTask.Show();

    return taskCompletionSource.Task;

}

1. Create a TaskCompletionSource with return type.
2. Set up your traditional async, but in the callback (done) event pass result on to TaskCompletionSource.
3. Return TaskCompletionSource.Task to waiting method.

To use this code simply:

private void DoPostButton_Click(object sender, RoutedEventArgs e)

{

    DoWhateverWithCamera();

}



public async void DoWhateverWithCamera()

{

    var result = await TakePicture();

   // Now do something with the result

}

This will not block GUI-thread, but return result on it. No need to use Dispatcher, dedicated background thread or async callback.