Bug 39691 - GKAgentDelegate implementors throws ArgumentException (unrecognized selector) if AgentWillUpdate is not implemented
Summary: GKAgentDelegate implementors throws ArgumentException (unrecognized selector)...
Alias: None
Product: iOS
Classification: Xamarin
Component: Xamarin.iOS.dll ()
Version: XI 9.8 (tvOS / C7)
Hardware: PC Mac OS
: Low minor
Target Milestone: Untriaged
Assignee: Alex Soto [MSFT]
Depends on:
Reported: 2016-03-16 19:41 UTC by Larry O'Brien
Modified: 2016-03-23 21:01 UTC (History)
2 users (show)

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

UIViewController to be swapped in to "Spritekit Game" iOS template (2.42 KB, application/octet-stream)
2016-03-16 19:41 UTC, Larry O'Brien
Xamarin.iOS Test Case (10.77 KB, application/zip)
2016-03-23 20:34 UTC, Alex Soto [MSFT]
Xcode ObjC Test Case (25.91 KB, application/zip)
2016-03-23 20:35 UTC, Alex Soto [MSFT]

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Description Larry O'Brien 2016-03-16 19:41:42 UTC
Created attachment 15434 [details]
UIViewController to be swapped in to "Spritekit Game" iOS template

Given a GKAgentDelegate :

public class SimpleDelegate : GKAgentDelegate 
  public override void AgentDidUpdate(GKAgent agent)
  /* Uncomment to cause runtime exception
  public override void AgentWillUpdate(GKAgent agent)

triggered via code similar to:

			agent = new GKAgent2D ();
			agent.Delegate = new SimpleDelegate ();
			entity = new GKEntity();

			agent.MaxSpeed = 10;
			var rammingSpeed = GKGoal.GetGoalToReachTargetSpeed(agent.MaxSpeed);
			agent.Behavior = GKBehavior.FromGoal(rammingSpeed, 1.0f);

creates a runtime exception (Argument exception, unknown selector, etc.)

This exception can be avoided by implementing `AgentWillUpdate` in user code. 

Repro steps:
     Create a new iOS "SpriteKit Game" from template
     Replace the generated viewcontroller with the attached (fix namespace)
     Run to create exception.

     Uncomment PositionTrackingAgent.AgentWillUpdate and run again.
     No exception
Comment 1 Larry O'Brien 2016-03-16 19:42:44 UTC
Argh. It should read "Uncomment to *avoid* runtime exception"
Comment 2 Sebastien Pouliot 2016-03-17 02:19:58 UTC
Foundation.MonoTouchException: Objective-C exception thrown.  Name: NSInvalidArgumentException Reason: -[bug39691_PositionTrackingDelegate agentWillUpdate:]: unrecognized selector sent to instance 0x7beba040
Native stack trace:
	0   CoreFoundation                      0x00960a14 __exceptionPreprocess + 180
	1   libobjc.A.dylib                     0x0898ee02 objc_exception_throw + 50
	2   CoreFoundation                      0x00969d63 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
	3   libobjc.A.dylib                     0x089a3196 -[NSObject forwardInvocation:] + 66
	4   CoreFoundation                      0x008a7488 ___forwarding___ + 472
	5   CoreFoundation                      0x008a728e _CF_forwarding_prep_0 + 14
	6   GameplayKit                         0x0894e24c -[GKAgent2D updateWithDeltaTime:] + 77
	7   GameplayKit                         0x0893a89b -[GKEntity updateWithDeltaTime:] + 258

It did not see it documented but looks like both selectors needs to be implemented. I get similar results if both are commented or the other one.

* They are declared as @optional in Apple's headers files and I did not see any web docs describing such requirement.

That really looks like an Apple bug and will need an ObjC sample to confirm / file rdar with them. Reducing priority (there's a workaround and it's unlikely _we_ can fix this)
Comment 3 Sebastien Pouliot 2016-03-23 15:04:05 UTC
@Alex, once bindings for watchOS 2.2 are completed can you verify (in ObjC) that this issue is an undocumented requirement from Apple ? thanks
Comment 4 Alex Soto [MSFT] 2016-03-23 20:34:28 UTC
Created attachment 15511 [details]
Xamarin.iOS Test Case

Xamarin.iOS Test Case
Comment 5 Alex Soto [MSFT] 2016-03-23 20:35:55 UTC
Created attachment 15512 [details]
Xcode ObjC Test Case

I can reproduce the same issue in this ObjC test case which is a line by line port of the C# one

Native Exception log:
Comment 6 Alex Soto [MSFT] 2016-03-23 21:01:47 UTC
Opened radar://25322551 with apple and it is being tracked in our trello board