Objective-C: Where to remove observer for NSNotification?

Question

I have an objective C class. In it, I created a init method and set up a NSNotification in it

//Set up NSNotification
[[NSNotificationCenter defaultCenter] a         


        

Answer 1

In general I put it into the dealloc method.

Answer 2

SWIFT 3

There are two cases of using notifications: - they are needed only when the view controller is on screen; - they are needed always, even if user opened another screen over current.

For the first case the correct place to add and remove observer are:

/// Add observers
///
/// - Parameter animated: the animation flag
override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    NotificationCenter.default.addObserver(...)
}

/// Remove observers
///
/// - Parameter animated: the animation flag
override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    NotificationCenter.default.removeObserver(self)
}

for the second case the correct way is:

/// Add observers
override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver(...)
}

/// Remove observers
///
/// - Parameter animated: the animation flag
override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    if self.isBeingDismissed // remove only when view controller is removed disappear forever
    || !(self.navigationController?.viewControllers.contains(self) ?? true) {
        NotificationCenter.default.removeObserver(self)
    }
}

And never put removeObserver in deinit{ ... } - it's a MISTAKE!