An -observeValueForKeyPath:ofObject:change:context: message was received but not handled
I am relatively new to KVO, so there is a good chance that I am violating some fundamental rule. I am using Core Data.
My app crashes with the following message: And what I can't understand is why a CGImage is getting involved in observing a value that is set on a MeasurementPointer object.
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '<CGImage 0x276fc0>: An -observeValueForKeyPath:ofObject:change:context: message was received but not handled.
Key path: measurementDescriptor
Observed object: <MeasurementPointer: 0x8201640> (entity: MeasurementPointer; id: 0x8200410 <x-coredata://EBEE0687-D67D-4B03-8C95-F4C60CFDC20F/MeasurementPointer/p75> ; data: {
measurementDescriptor = "0x260fd0 <x-coredata://EBEE0687-D67D-4B03-8C95-F4C60CFDC20F/MeasurementDescriptor/p22>";
})
Change: {
kind = 1;
new = "<MeasurementDescriptor: 0x262530> (entity: MeasurementDescriptor; id: 0x260fd0 <x-coredata://EBEE0687-D67D-4B03-8C95-F4C60CFDC20F/MeasurementDescriptor/p22> ; data: {\n measurementName = Temperature;\n measurementUnits = \"\\U00b0C\";\n sortString = nil;\n})";
}
Context: 0x0'
*** Call stack at first throw:
(
0 CoreFoundation 0x30897ed3 __exceptionPreprocess + 114
1 libobjc.A.dylib 0x3002f811 objc_exception_throw + 24
2 CoreFoundation 0x30897d15 +[NSException raise:format:arguments:] + 68
3 CoreFoundation 0x30897d4f +[NSException raise:format:] + 34
4 Foundation 0x34a13779 -[NSObject(NSKeyValueObserving) observeValueForKeyPath:ofObject:change:context:] + 60
5 Foundation 0x349b6acd NSKeyValueNotifyObserver + 216
6 Foundation 0x349b6775 NSKeyValueDidChange + 236
7 Foundation 0x349ae489 -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] + 76
8 CoreData 0x3165b577 _PF_ManagedObject_DidChangeValueForKeyIndex + 102
9 CoreData 0x3165ac51 _sharedIMPL_setvfk_core + 184
10 CoreData 0x3165dc83 _svfk_0 + 10
11 SPARKvue 0x000479f1 -[MeasurementViewController doneAction:] + 152
12 CoreFoundation 0x3083f719 -[NSObject(NSObject) performSelector:withObject:withObject:] + 24
13 UIKit 0x31eb1141 -[UIApplication sendAction:to:from:forEvent:] + 84
14 UIKit 0x31f08315 -[UIBarButtonItem(UIInternal) _sendAction:withEvent:] + 92
15 CoreFoundation 0x3083f719 -[NSObject(NSObject) performSelector:withObject:withObject:] + 24
16 UIKit 0x31eb1141 -[UIApplication sendAction:to:from:forEvent:] + 84
17 UIKit 0x31eb10e1 -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 32
18 UIKit 0x31eb10b3 -[UIControl sendAction:to:forEvent:] + 38
19 UIKit 0x31eb0e05 -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 356
20 UIKit 0x31eb1453 -[UIControl touchesEnded:withEvent:] + 342
21 UIKit 0x31eafddd -[UIWindow _sendTouchesForEvent:] + 368
22 UIKit 0x31eaf757 -[UIWindow sendEvent:] + 262
23 UIKit 0x31eaa9ff -[UIApplication sendEvent:] + 298
24 UIKit 0x31eaa337 _UIApplicationHandleEvent + 5110
25 GraphicsServices 0x31e4504b PurpleEventCallback + 666
26 CoreFoundation 0x3082cce3 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 26
27 CoreFoundation 0x3082cca7 __CFRunLoopDoSource1 + 166
28 CoreFoundation 0x3081f56d __CFRunLoopRun + 520
29 CoreFoundation 0x3081f277 CFRunLoopRunSpecific + 230
30 CoreFoundation 0x3081f17f CFRunLoopRunInMode + 58
31 GraphicsServices 0x31e445f3 GSEventRunModal + 114
32 GraphicsServices 0x31e4469f GSEventRun + 62
33 UIKit 0x31e51123 -[UIApplication _run] + 402
34 UIKit 0x31e4f12f UIApplicationMain + 670
35 SPARKvue 0x000031ff main + 70
36 SPARKvue 0x000031b4 start + 40
)
terminate called after throwing an instance of 'NSException'
Program received signal: “SIGABRT”.
All that is happening to trigger this is:
[[self measurementPointer] setMeasurementDescriptor:descriptor];
Given this,
[[meterDisplay measurementPointer] addObserver:self
forKeyPath:@"measurementDescriptor"
options:NSKeyValueObservingOptionNew
context:nil];
Basically, MeasurementPointer objects point to MeasurementDescriptor objects - and both are NSManagedObject subclasses. MeasurementDescriptor objects describe a specific 'measurement' and 'unit' combination (e.g., "Temperature (°C)" or "Wind Speed (mph)"). MeasurementDescriptors are something like singletons to the extent that there is only one for each unique measurement-unit combo.
MeasurementPointers are referenced by other objects - both Model objects and Controller objects. A MeasurementPointer references a MeasurementDescriptor. Many objects are interested in knowing when a MeasurementPointer starts referencing a new/different MeasurementDescriptor. Such a change might cause a graph display's axis to change, for example. Or, in the code above, might cause a meter display to show a different sample (from a selected set of samples).
I think that fundamental problem is that a CGImage is receiving a message that is not intended for it... unfortunately, this is intermittent, so I have not been able to find a pattern that triggers it.
Answer
You have an object that got dealloc'ed and did not stop observing another object. Walk through all of your -addObserver... calls and make sure they are matched with -removeObserver... calls at least in the -dealloc and possibly in the -viewDidUnload depending on your application structure.