In iOS 11, you don’t have to. Just let the observer go out of scope. There is no penalty any longer for letting an observer die before the observed or for letting the observed die before the observer, so you have no actual work to do. On the other hand, if you really want to … Read more
You need to implement the indexed array accessors as defined in the KVC programming guide. Then you must use those accessors to access the array and the KVO triggering will work. You can also call -mutableArrayValueForKey: and use that array to addObject: and such and it will in turn call the accessor methods and the … Read more
UIKit is mostly NOT KVO compliant. This is mostly because UIView acts as high-level wrapper for CALayer, so when you eg. change the frame property of an UIView, it will change the layers frame but leave eg. the bounds property of the UIView untouched, so no observer will be triggered for the view.bounds path, because … Read more
Short answer: No. Long answer: Nothing in UIKit is guaranteed to be KVO-compliant. If you happen to find that KVO-ing a property works, be grateful, it’s unintentional. Also: be wary. It could very well break in the future. If you find that this is something you need, please file an enhancement request. About your actual … Read more
But shouldn’t the synthesized accessors automatically return such a proxy object? No. What’s the proper way to work around this–should I write a custom accessor that just invokes [super mutableArrayValueForKey…]? No. Implement the array accessors. When you call these, KVO will post the appropriate notifications automatically. So all you have to do is: [myObject insertObject:newObject … Read more
You still can implement -dealloc under ARC, which appears to be the appropriate place to remove the observation of key values. You just don’t call [super dealloc] from within this method any more. If you were overriding -release before, you were doing things the wrong way.
Use a delegate if you want to talk to only one object. For example, a tableView has a delegate – only one object should be responsible for dealing with it. Use notifications if you want to tell everyone that something has happened. For example in low memory situations a notification is sent telling your app … Read more
Encapsulation If the ivar is private, the other parts of the program can’t get at it as easily. With a declared property, the clever people can access and mutate quite easily via the accessors. Performance Yes, this can make a difference in some cases. Some programs have constraints where they can not use any objc … Read more
There are usually notifications or other observable events where KVO isn’t supported. Even though the docs says ‘no’, it is ostensibly safe to observe the CALayer backing the UIView. Observing the CALayer works in practice because of its extensive use of KVO and proper accessors (instead of ivar manipulation). It’s not guaranteed to work going … Read more
You can use KVO in Swift, but only for dynamic properties of NSObject subclass. Consider that you wanted to observe the bar property of a Foo class. In Swift 4, specify bar as dynamic property in your NSObject subclass: class Foo: NSObject { @objc dynamic var bar = 0 } You can then register to … Read more