Question

Sorry about not being able to give a more precise headline, but here is what I want to do. I have a method foo which will initiate some UI animations. When these animations are finished, I want to signal completion of the method. But instead of signaling completion through an event, I would like to make the method awaitable. How can this be done?

void foo()
{  
  // start some animations 
   storyboard.Begin();
   storyboard.Completed += (s, e) => { // signal that foo has completed }
}

calling code should be able to write:

await foo();

My actual foo is more complex than illustration above, in that I have a series of animations, which occur one after another, and foo is supposed to complete when all animations are completed.

Answer 1

Generally things that complete based on an event get ‘wrapped’ by using a TaskCompletionSource. Unfortunately, the example on MSDN is (IMHO) overly complicated instead of just being a single instance+event. You’d have something like:

public Task Foo()
{
    var tcs = new TaskCompletionSource<bool>();
    storyboard.Begin();
    storyboard.Completed += (s, e) => tcs.SetResult(true);
    return tcs.Task;
}

In this scenario, there’s no real need for the TResult, but TaskCompletionSource doesn’t appear to have a non-generic version and I’m not sure what the equivalent pattern would be