FLEXTool/FLEX

Cannot remove an observer <FLEXExplorerViewController 0x10aa28570> for the key path "frame" from <LWindow 0x11011e800> because it is not registered as an observer.

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#371 opened on Jan 20, 2020

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 (5 comments) (0 reactions) (0 assignees)Objective-C (14,597 stars) (1,777 forks)batch import
bugcan't reproducehelp wanted

Description

(Crash in Lockscreen using FLEXing)

Date: 1/20/20, 4:43 PM
Process: SpringBoard
Bundle id: com.apple.springboard
Device: iPhone XS Max, iOS 12.4
 
Exception type: NSRangeException
Reason: Cannot remove an observer <FLEXExplorerViewController 0x10aa28570> for the key path "frame" from <LWindow 0x11011e800> because it is not registered as an observer.
Culprit: libFLEX.dylib
Call stack:
0   CoreFoundation     0x1c4a7ead0 __exceptionPreprocess
1   libobjc.A.dylib    0x1c3c83d00 objc_exception_throw
2   CoreFoundation     0x1c49842f4 -[NSCache init]
3   Foundation         0x1c5437f98 -[NSObject(NSKeyValueObserverRegistration) _removeObserver:forProperty:]
4   Foundation         0x1c5437d50 -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:]
5   libFLEX.dylib      0x109dbbc04 -[FLEXExplorerViewController stopObservingView:]
6   libFLEX.dylib      0x109dbb010 -[FLEXExplorerViewController setViewsAtTapPoint:]
7   libFLEX.dylib      0x109dbb308 -[FLEXExplorerViewController setCurrentMode:]
8   libFLEX.dylib      0x109dbcc88 -[FLEXExplorerViewController closeButtonTapped:]
9   libobjc.A.dylib    0x1c3c7f760 -[NSObject performSelector:withObject:withObject:]
10  UIKitCore          0x1f1ea6e88 -[UIApplication sendAction:to:from:forEvent:]
11  UIKitCore          0x1f192b1dc -[UIControl sendAction:to:forEvent:]
12  UIKitCore          0x1f192b510 -[UIControl _sendActionsForEvents:withEvent:]
13  UIKitCore          0x1f192a524 -[UIControl touchesEnded:withEvent:]
14  UIKitCore          0x1f1edfd28 -[UIWindow _sendTouchesForEvent:]
15  UIKitCore          0x1f1ee0f60 -[UIWindow sendEvent:]
16  UIKitCore          0x1f1ec01e8 -[UIApplication sendEvent:]
17  UIKitCore          0x1f1f8b3e8 __dispatchPreprocessedEventFromEventQueue
18  UIKitCore          0x1f1f8dba4 __handleEventQueueInternal
19  UIKitCore          0x1f1f8df14 __handleEventQueueInternal
20  UIKitCore          0x1f1f8df14 __handleEventQueueInternal
21  UIKitCore          0x1f1f8df14 __handleEventQueueInternal
22  UIKitCore          0x1f1f86c5c __handleHIDEventFetcherDrain
23  CoreFoundation     0x1c4a0eb54 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
24  CoreFoundation     0x1c4a0ead0 __CFRunLoopDoSource0
25  CoreFoundation     0x1c4a0e38c __CFRunLoopDoSources0
26  CoreFoundation     0x1c4a09060 __CFRunLoopRun
27  CoreFoundation     0x1c4a08964 CFRunLoopRunSpecific
28  GraphicsServices   0x1c6c49d8c GSEventRunModal
29  UIKitCore          0x1f1ea5758 UIApplicationMain
30  FrontBoard         0x1dabee11c FBSystemAppMain
31  SpringBoard        0x103088da4 SpringBoard + 2051492
32  libdyld.dylib      0x1c44c4fd8 start

Contributor guide

Tech stack
objective c
Domain
mobile
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Objective C basicsUnderstanding of KVO
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
The crash occurs in ` [FLEXExplorerViewController stopObservingView:]` when trying to remove an observer for key path "frame". Investigate the `stopObservingView:` method to ensure that `removeObserver:forKeyPath:` is only called if the observer was previously registered. Check the `startObservingView:` method to see if observations are properly paired. Consider adding a flag or using `NSKeyValueObservingOptionPrior` to avoid duplicate removal. Look at the GitHub issue comments for additional context or proposed fixes.