NSNotificationCenter: Removing an Observer in Swift

nsnotificationcenter, swift

Solution

When you use the 'blocks' based approach to observing notifications then `self` isn't in fact the observer. The function returns an object which acts as the observer:

func addObserverForName(_ name: String?,
                 object obj: AnyObject?,
                  queue queue: NSOperationQueue?,
             usingBlock block: (NSNotification!) -> Void) -> NSObjectProtocol

You need to keep a reference to this returned object and pass it in as the observer when you call `removeObserver`

It's explained well in the Apple Doc here

Problem

I have a view controller with a button. When the button is pressed it adds an observer, like so: ``` func buttonPress(sender:UIButton){ NSNotificationCenter.defaultCenter().addObserverForName("buttonPressEvent", object:nil, queue:nil, usingBlock:{(notif) -> Void in // code }) } ``` When I dismiss this view controller, and then return to it and press the button the `//code` is executed twice. If I go away and come back again the `//code` is executed three times, and so on. What I want to do is to remove the Observer before I add it again, so this code doesn't execute twice. Ive gone through the documentation here and Ive added this line of code just above where I add the Observer: ``` NSNotificationCenter.defaultCenter().removeObserver(self, name:"buttonPressEvent", object:nil) ``` But this isnt working. Can anyone tell me where I'm going wrong?

Original source