NotificationCenter Functions

When assigning a function to a NotificationCenter, it must:

• Include the notification object in its signature.
• Never be called directly from your code.

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Example

Good

func method(calledFrom notification: NSNotification) {
    // It's clear that this method is going to be called from a notification.
}

NotificationCenter.default.addObserver(self, selector: #selector(method(calledFrom:)), name: "GoodExample", object: nil)

Bad

func method() {
    // You can't know if this method was called from a notification or from somewhere else...
}

NotificationCenter.default.addObserver(self, selector: #selector(method), name: "BadExample", object: nil)

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Motivation

• Separation of concerns. You can easily separate out which methods are expected to be called by notification center and which are not.
• It avoids confusions.
• It prevents runtime crashes that may be caused by removing a method that you might think is not being used, but it's actually being called by notification center at runtime.
• By appending an Notification object to the method signature, you won't be able to call it from your code, because you won't have a notification object to pass in.