Crash in stopFlow(immediately immediately: Bool = false, userDidSkip skipped: Bool = false, shouldCallDelegate: Bool = true )

[swetaarya]

0 libswiftCore.dylib 0x100fb04ac hidden#8277 (_hidden#7745:75)
1 libswiftCore.dylib 0x100fbe3fc swift_unknownUnownedTakeStrong (_hidden#9593:764)
2 Instructions 0x100b1acc8 FlowManager.(stopFlow(immediately : Bool, userDidSkip : Bool, shouldCallDelegate : Bool) -> ()).(closure #2) + 412
3 UIKit 0x1969c9cf8 -[UIViewAnimationBlockDelegate _didEndBlockAnimation:finished:context:] + 492
4 UIKit 0x1969c981c -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] + 312
5 UIKit 0x1969c965c -[UIViewAnimationState animationDidStop:finished:] + 160
6 QuartzCore 0x193e4a180 CA::Layer::run_animation_callbacks(void*) + 260
7 libdispatch.dylib 0x18f9c11c0 _dispatch_client_callout + 16
8 libdispatch.dylib 0x18f9c5d6c _dispatch_main_queue_callback_4CF + 1000
9 CoreFoundation 0x190ae3f2c CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE + 12
10 CoreFoundation 0x190ae1b18 __CFRunLoopRun + 1660
11 CoreFoundation 0x190a10048 CFRunLoopRunSpecific + 444
12 GraphicsServices 0x192496198 GSEventRunModal + 180
13 UIKit 0x1969fc2fc -[UIApplication _run] + 684
14 UIKit 0x1969f7034 UIApplicationMain + 208
15 Shop101 0x1003fdafc main (AppDelegate.swift:31)
16 libdispatch.dylib 0x18f9f45b8 (Missing)

[swetaarya]

Could u please tell me, what is happening here.

[ephread]

Hello @swetaarya, sadly from such stack trace, without more context attached to it, I'm afraid I can't really tell you issue right away. What action lead the crash?

[swetaarya]

i think FlowManager.(stopFlow(immediately : Bool, userDidSkip : Bool, shouldCallDelegate : Bool) -> ()).(closure #2) + 412 causing crash

[swetaarya]

i was calling CoachMarkController.startOn(self) in viewDidLoad() method. May be this causing problem

[ephread]

That's extremely likely, you need to call startOn from viewDidAppear, as the view hierarchy needs to be ready. ;)

[swetaarya]

But why crash occuring in FlowManager.(stopFlow(immediately : Bool, userDidSkip : Bool, shouldCallDelegate : Bool) -> ()).(closure #2) + 412

[ephread]

Certainly because of a nil pointer inside stopFlow, either self or self.coachMarksViewController (see here). This stack trace seems to indicate that the parent object was somehow deallocated and the closure lived its short and unhappy life by itself. But again, without more context (some of the code you're using, or which action lead to the crash) I can't be of any more help.

[anfriis]

I just had this crash in my app too.
I think I was quickly closing and opening some view controllers, and calling stop(immediately: true) when closing a view controller.

When looking into the coachMarksViewController property in the FlowManager, I can see that it is marked as unowned. I looked in the Apple documentation for unowned and it says

If you try to access the value of an unowned reference after that instance has been deallocated, you’ll get a runtime error.

So I suspect that the coachMarksViewController was deallocated and maybe we should consider making it weak and optional instead, so we can avoid the crash?

[anfriis]

PR: #99

[anfriis]

I seems to be working in the PR I created, so can it be merged to master?

[ephread]

Thanks for the work @anfriis, I haven't merged your PR yet, because I believe that the block shouldn't normally outlive the controller (hence the use of unowned). I wanted to investigate beforehand. ;)

[anfriis]

No problem :) but i guess the block is outliving the controller because the controller gets deallocated when the containing view controller does, and then the block lives on somehow

[anfriis]

I can see that I now have a new problem, that the instructionsRootView is not removed from the app window, if the coachMarksViewController is nil when calling detachFromParentViewController(), so the instructions view is shown on the new page... So it would be great if you can investigate it :)

[halolee]

I could replicate the same issue by quickly opening and closing ViewControllers.

Based on the stack trace, the crash line points to FlowManager:126 self.coachMarksViewController.detachFromWindow(), which is an indication of using a deallocated self reference.

Further on @anfriis comment, I would propose to keep a weak self reference in the completionBlock instead of touching the unowned reference.

will submit a pull request shortly after.

        let completionBlock = { [weak self] (finished: Bool) -> Void in
            guard let strongSelf = self else { return }
            strongSelf.coachMarksViewController.detachFromWindow()
            if shouldCallDelegate { strongSelf.delegate?.didEndShowingBySkipping(skipped) }
        }

[ephread]

It seems #161 fixes the issue.

@anfriis and @halolee, thanks a lot for working on this and fixing the issue!
I'm now going to close #99 that I left dangling for too long instead of investigating the issue 😓.