Please point me in the correct direction to understand how to run in the background in iOS - ios

Question

I'm working on a fitness app (using Xamarin) and would like it to continue running in the background if the user switches to another app or pushes the side button to blank out the screen. I have looked at multiple tutorials, include this one https://robgibbens.com/backgrounding-with-xamarin-forms/, which seemed very promising. However, when running my app and switching to another application or blanking the screen, my app simply suspends. Hers is the iOS specific code that starts the background task:
public class IOSPlayWorkoutTask
{
nint _taskID;
CancellationTokenSource _cts;
Workout _workout;
public async Task Start()
{
_cts = new CancellationTokenSource();
_taskID = UIApplication.SharedApplication.BeginBackgroundTask("IOSPlayWorkoutTask", OnExpiration);
try
{
WorkoutPlayer.Shared.Workout = _workout;
await WorkoutPlayer.Shared.PlayWorkout(_cts.Token);
}
catch (OperationCanceledException)
{
}
finally
{
if (_cts.IsCancellationRequested)
{
//Device.BeginInvokeOnMainThread(
// () => MessagingCenter.Send(new CancelPlayingWorkoutMessage(), CancelPlayingWorkoutMessage.MessageText));
}
}
UIApplication.SharedApplication.EndBackgroundTask(_taskID);
}
public void Pause()
{
WorkoutPlayer.Shared.RequestPause();
_cts.Cancel();
Device.BeginInvokeOnMainThread(
() => MessagingCenter.Send(new PausedWorkoutMessage(), PausedWorkoutMessage.MessageText));
}
public void Stop()
{
_cts.Cancel();
Device.BeginInvokeOnMainThread(
() => MessagingCenter.Send(new FinishedWorkoutMessage(), FinishedWorkoutMessage.MessageText));
}
void OnExpiration()
{
_cts.Cancel();
}
public IOSPlayWorkoutTask(Workout w)
{
_workout = w;
}
}
The iOS app delegate registers to receive messages, one of which starts the task above. I know I must be missing something very basic. Any help would be greatly appreciated. I know this has to be possible based on my experience using other fitness apps like Couch to 5k.

Answer 1

Thanks #sushihangover and #Paulw11 for your input. Looks like the secret is adding a handler to BeginBackgroundTask that calls EndBackgroundTask. Not sure I understand fully at this point, but apparently this give iOS the impression that you are a "good citizen", but continues processing your task. Here is my code that works:
public async Task Start()
{
_cts = new CancellationTokenSource();
//_taskID = UIApplication.SharedApplication.BeginBackgroundTask("IOSPlayWorkoutTask", OnExpiration);
_taskID = UIApplication.SharedApplication.BeginBackgroundTask(() =>
{
Console.WriteLine("Guess my time is up");
UIApplication.SharedApplication.EndBackgroundTask(_taskID);
});
try
{
WorkoutPlayer.Shared.Workout = _workout;
await WorkoutPlayer.Shared.PlayWorkout(_cts.Token);
//finished = true;
}
catch (OperationCanceledException)
{
Console.WriteLine("OperationCanceledException");
//finished = true;
}
finally
{
if (_cts.IsCancellationRequested)
{
//Device.BeginInvokeOnMainThread(
// () => MessagingCenter.Send(new CancelPlayingWorkoutMessage(), CancelPlayingWorkoutMessage.MessageText));
}
}
UIApplication.SharedApplication.EndBackgroundTask(_taskID);
}