Bug 18560 - TaskScheduler.UnobservedTaskException raised for trapped exceptions from Task.Factory.FromAsync
Summary: TaskScheduler.UnobservedTaskException raised for trapped exceptions from Task...
Alias: None
Product: Class Libraries
Classification: Mono
Component: mscorlib ()
Version: 3.2.x
Hardware: PC Mac OS
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2014-03-24 17:52 UTC by Dave Dunkin
Modified: 2014-03-31 13:16 UTC (History)
3 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Dave Dunkin 2014-03-24 17:52:48 UTC
If an exception is thrown from async code adapted with Task.Factory.FromAsync and later caught, UnobservedTaskException is still raised. This is related to bug 17015.

Reproduced with Xamarin.iOS

using System;
using System.Threading.Tasks;
using MonoTouch.UIKit;
using MonoTouch.Foundation;

namespace UnhandledExceptionRepro
	public partial class UnhandledExceptionReproViewController :
		public UnhandledExceptionReproViewController(IntPtr handle)
			: base(handle)

		public override async void ViewDidLoad()

			TaskScheduler.UnobservedTaskException += (sender, e) =>
				if (e.Exception != null)
					InvokeOnMainThread(() =>
						new UIAlertView("unobserved task exception",
							e.Exception.Message, null, "Ok", null).Show());

				await getResult();
			catch (Exception ex)
				new UIAlertView("trapped exception", ex.Message, null, "Ok",

		private async Task getResult()
			await Task.Delay(10);

			await Task.Factory.FromAsync(BeginFoo(), EndFoo);

		IAsyncResult BeginFoo()
			Action foo = () => {};
			AsyncCallback cb = _ => {};
			return foo.BeginInvoke(cb, null);

		void EndFoo(IAsyncResult result)
			throw new Exception("boom");
Comment 1 Marek Safar 2014-03-31 13:16:16 UTC
This issue is already fixed in Xamarin.iOS 7.2.1 or newer