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Why is this code not KVO-Compliant?
@interface ILViewController : NSViewController

- (ILWindowController *)windowController;

@end

@implementation ILViewController

- (NSWindowController *)windowController {
    return self.view.window.windowController;
}

- (void)setView:(NSView *)view {
    [self willChangeValueForKey:@"windowController"];
    [super setView:view];
    [self didChangeValueForKey:@"windowController"];
}

@end

Cannot update for observer <NSAutounbinderObservance 0x1005cf990> for the key path
"windowController.mainStatus" from <ILViewController 0x1001976b0>, most likely because
the value for the key "windowController" has changed without an appropriate KVO
notification being sent. Check the KVO-compliance of the ILViewController class.

@interface ILViewController : NSViewController {
    ILWindowController *_windowController;
}

- (ILWindowController *)windowController;

@end

@implementation ILViewController

- (NSWindowController *)windowController {
    return _windowController;
}

- (void)setView:(NSView *)view {
    [super setView:view];
    _windowController = view.window.windowController;
}

@end

KVO autonotifying only supports -set<Key>: methods that return void. Autonotifying
will not be done for invocations of -[NSView _setWindow:].
Cannot remove an observer <NSKeyValueObservance 0x102e17880> for the key path
"window.windowController.mainStatus" from <NSView 0x102e13ec0>, most likely because
the value for the key "window" has changed without an appropriate KVO notification
 being sent. Check the KVO-compliance of the NSView class.