NSNotification userinfo keeps stacking when pushing buttons

Question

So I have two viewcontrollers, which are shown at the same time. The goal is the following: when I press the menu, it gives back an index. This will notify the other screen that it needs to update.

I am doing the following:

Controller A (the menu)

   func carbonTabSwipeNavigation(carbonTabSwipeNavigation: CarbonTabSwipeNavigation, didMoveAtIndex index: UInt) {
    //NSLog("Did move at index: %ld", index)
        //NSNotification to send data
        NSNotificationCenter.defaultCenter().postNotificationName(NotificationNames.GetIndexCarbonKit, object: nil, userInfo: ["clickedIndex" : Int(index)])
}

Controller B (the receiver)

override func viewWillAppear(animated: Bool) {
    NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(SearchResults.didReceiveNotification(_:)), name: NotificationNames.GetIndexCarbonKit, object: nil)
}


func didReceiveNotification(notification: NSNotification) {
    let index:Dictionary<String,Int> = notification.userInfo as! Dictionary<String,Int>
    let messageFromNotification = index["clickedIndex"]
    print(" SearchResults now shows index: \(messageFromNotification)")
}

My issue is the following: the Dictionary in which I'm sending the index from A to B, keeps stacking. So if I press the menu multiple times, my output is the following:

 SearchResults now shows index: Optional(0)
 SearchResults now shows index: Optional(1)
 SearchResults now shows index: Optional(1)
 SearchResults now shows index: Optional(2)
 SearchResults now shows index: Optional(2)
 SearchResults now shows index: Optional(2)
 SearchResults now shows index: Optional(3)
 SearchResults now shows index: Optional(3)
 SearchResults now shows index: Optional(3)
 SearchResults now shows index: Optional(3)
 SearchResults now shows index: Optional(1)
 SearchResults now shows index: Optional(1)
 SearchResults now shows index: Optional(1)
 SearchResults now shows index: Optional(1)
 SearchResults now shows index: Optional(1)

How can I only get the last index? I don't need a stack of the others.

Answer 1

Found the correct answer myself. Apparently all I had to do was add the NotificationCenter to the ViewWillAppear, and remove it at the ViewWillDisappear. When I switch in the menu between the views (which is 4 times the same view) it only gives back one value.

override func viewWillAppear(animated: Bool) {
    NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(SearchResults.didReceiveNotification(_:)), name: NotificationNames.GetIndexCarbonKit, object: nil)
}

override func viewWillDisappear(animated: Bool) {
    NSNotificationCenter.defaultCenter().removeObserver(self)
}

func didReceiveNotification(notification: NSNotification) {
    let index:Dictionary<String,Int> = notification.userInfo as! Dictionary<String,Int>
    self.currentIndex = (index.first?.1)!
    print(currentIndex)
}