Using a TaskCompletionSource to enable async and await together with UIAlertController. From: http://www.hjerpbakk.com/blog/2014/11/23/from-uialertview-to-uialertcontroller-using-xamarin-and-async-await

CustomerFeelingSheet.cs

public static class CustomerFeelingSheet {
  public static Task<CustomerFeeling> ShowRatingDialogAsync(UIViewController parent) {
    var taskCompletionSource = new TaskCompletionSource<CustomerFeeling>();

    var alert = UIAlertController.Create("howDoYouFeel".T(), null, UIAlertControllerStyle.ActionSheet);

    alert.AddAction(UIAlertAction.Create("likeIt".T(), UIAlertActionStyle.Default,
        a => taskCompletionSource.SetResult(CustomerFeeling.LikeIt)));
    alert.AddAction(UIAlertAction.Create("couldBeBetter".T(), UIAlertActionStyle.Default,
        a => taskCompletionSource.SetResult(CustomerFeeling.CouldBeBetter)));
    alert.AddAction(UIAlertAction.Create("cancel".T(), UIAlertActionStyle.Cancel,
        a => taskCompletionSource.SetResult(CustomerFeeling.DontCare)));

    parent.PresentViewController(alert, true, null);
    return taskCompletionSource.Task;
  }
}