NSUndoManager removeAllActionsWithTarget crash - ios

Question

I have some abbreviated iOS Objective-C sample code (simplified from a larger project) that causes a crash in NSUndoManager that I can't explain.
Namely, when an object that is only held onto by the NSUndoManager deallocs (because it's beyond the levels of undo), and, according to the docs calls removeAllActionsWithTarget:self, I get an EXC_BAD_ACCESS.
// SimpleViewController.m
#interface ViewController ()
#property (nonatomic, strong) NSUndoManager *undoManager;
#end
#implementation ViewController
#synthesize undoManager;
// called from a simple button
- (IBAction)doItTapped:(id)sender
{
CoolObject *object = [CoolObject new];
object.undoManager = self.undoManager;
// according to docs, object will be retained by NSUndoManager here
// but target will not (which should be okay)
[self.undoManager registerUndoWithTarget:self selector:#selector(notCool:) object:object];
}
- (void)viewDidLoad
{
[super viewDidLoad];
self.undoManager = [NSUndoManager new];
self.undoManager.levelsOfUndo = 3;
}
and
// CoolObject.m
#implementation CoolObject
- (void)dealloc
{
[self.undoManager removeAllActionsWithTarget:self];
}
#end
After the 4th tap of the button (levelsOfUndo + 1), it crashes.
If I swap NSUndoManager with GCUndoManager, no crash.
Tested in iOS 10.2 sim and devices.
Thanks for any ideas!

Answer 1

Their are chances that you might be getting this error because self.undoManager is not retained at that point where you are using it. When the object is already deallocated and you try to access it, you will get bad access exception.
Try to change your code from this:
CoolObject *object = [CoolObject new];
to this:
#interface ViewController (){
CoolObject *object;
}
#property (nonatomic, strong) NSUndoManager *undoManager;
#end
#implementation ViewController
- (IBAction)doItTapped:(id)sender
{
object = [CoolObject new];
object.undoManager = self.undoManager;
// according to docs, object will be retained by NSUndoManager here
// but target will not (which should be okay)
[self.undoManager registerUndoWithTarget:self selector:#selector(notCool:) object:object];
}
#end
Hope this will help.

Answer 2

Just like me, you seem to have misinterpreted the admittedly inaccurately written documentation. The docs talk about "target", "object" and "target object" as if they were different things when they really mean exactly one and the same: the (id)target parameter of -removeAllActionsWithTarget:
In other words, in my opinion you should not need to call -removeAllActionsWithTarget: inside of CoolObject at all because CoolObject has been specified as the object of -registerUndoWithTarget:selector:object: whereas the target is your ViewController.
You may have to call -removeAllActionsWithTarget: in your NSViewController's -dealloc but even that is unnecessary in your example because your NSViewController owns the NSUndoManager and thus ViewController won't go away before undoManager does.