NSUndoManager errors with "unrecognized selector sent to instance" - ios

Question

Working on implementing NSUndoManager within an iOS9 app. Current undo code looks like this:
func setActiveColorData(colorData: ColorData) {
if colorData != activeColorData {
print(self)
undoManager?.registerUndoWithTarget(self, selector: "setActiveColorData:", object: activeColorData!)
undoManager?.setActionName("Change color")
print("Set undo action")
activeColorData = colorData
}
}
ColorData is just a simple class with three floats inside of it (hue, saturation, brightness) and some utility methods.
Everything works fine, including the shake gesture which brings up the undo prompt. But once you click undo, the app crashes and the following error:
2016-02-25 16:26:58.225 Color[89399:5503615] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Color.PickerViewController setActiveColorData:]: unrecognized selector sent to instance 0x7fa080776820'
*** First throw call stack:
(
0 CoreFoundation 0x0000000105b75e65 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x0000000108159deb objc_exception_throw + 48
2 CoreFoundation 0x0000000105b7e48d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3 CoreFoundation 0x0000000105acb90a ___forwarding___ + 970
4 CoreFoundation 0x0000000105acb4b8 _CF_forwarding_prep_0 + 120
5 Foundation 0x00000001066b2feb -[_NSUndoStack popAndInvoke] + 261
6 Foundation 0x00000001066b2162 -[NSUndoManager undoNestedGroup] + 424
7 UIKit 0x0000000106c46813 -[UIApplication alertView:clickedButtonAtIndex:] + 151
8 UIKit 0x0000000106f63589 -[UIAlertView _prepareToDismissForTappedIndex:] + 136
9 UIKit 0x0000000106f62fc7 __35-[UIAlertView _prepareAlertActions]_block_invoke50 + 53
10 UIKit 0x0000000106f54572 -[UIAlertController _dismissAnimated:triggeringAction:triggeredByPopoverDimmingView:] + 133
11 UIKit 0x0000000107604eb6 -[_UIAlertControllerView _handleActionSelectionGestureRecognizer:] + 694
12 UIKit 0x000000010711ee73 _UIGestureRecognizerSendTargetActions + 153
13 UIKit 0x000000010711b4e5 _UIGestureRecognizerSendActions + 162
14 UIKit 0x00000001071194e2 -[UIGestureRecognizer _updateGestureWithEvent:buttonEvent:] + 843
15 UIKit 0x00000001071219a0 ___UIGestureRecognizerUpdate_block_invoke904 + 79
16 UIKit 0x000000010712183e _UIGestureRecognizerRemoveObjectsFromArrayAndApplyBlocks + 342
17 UIKit 0x000000010710f101 _UIGestureRecognizerUpdate + 2634
18 UIKit 0x0000000106ca6f8a -[UIWindow _sendGesturesForEvent:] + 1137
19 UIKit 0x0000000106ca81c0 -[UIWindow sendEvent:] + 849
20 UIKit 0x0000000106c56b66 -[UIApplication sendEvent:] + 263
21 UIKit 0x0000000106c30d97 _UIApplicationHandleEventQueue + 6844
22 CoreFoundation 0x0000000105aa1a31 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
23 CoreFoundation 0x0000000105a9795c __CFRunLoopDoSources0 + 556
24 CoreFoundation 0x0000000105a96e13 __CFRunLoopRun + 867
25 CoreFoundation 0x0000000105a96828 CFRunLoopRunSpecific + 488
26 GraphicsServices 0x000000010a416ad2 GSEventRunModal + 161
27 UIKit 0x0000000106c36610 UIApplicationMain + 171
28 Color 0x00000001052a2a7d main + 109
29 libdyld.dylib 0x0000000108c9992d start + 1
30 ??? 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
I've check the PickerViewController instance and the memory locations match up (from the print(self) line, in this case 0x7fa080776820). Any idea why it can't invoke this selector? Or is it something else? Thanks!

Answer 1

I'm seeing this same kind of crash in a photo editing app when memory is running low. When I get a memory warning, I clear the undo manager but in my case I believe this crash happens because the memory is getting deleted out from under the undo manager.
In case it's related: https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/UndoArchitecture/Articles/CleaningUndoStack.html