CODEWITHSUNDEEP
iosswiftkey-value-observing
tahoecoop
tahoecoop

Reputation: 378

How to remove KVO observer from tableViewCell?

I know this probably isn't best practice for MVC but I have an observer in my custom tableViewCell to know when I am expanded the cell or not (code below). When I press the back button on my nav bar, the app crashes with "An instance TableViewCell was deallocated while key value observers were still registered with it." How can I check if a cell is observing, and how to remove observer when user hits that back button? Thanks a lot!!!

class ClientDetailTableViewCell: UITableViewCell {

   // Sets default and expanded cell heights
   class var expandedHeight:CGFloat { get { return 150 } }
   class var defaultHeight:CGFloat { get { return 50 } }

   // sets to check if a row has been clicked
   var frameAdded = false

   // checks if height to see if buttons are hidden
   func checkHeight () {

      button1.hidden = (frame.size.height < PersonTableViewCell.expandedHeight)
   }

   // Start Key Value Observing
   func watchFrameChanges() {

      if(!frameAdded) {

         addObserver(self, forKeyPath: "frame", options: NSKeyValueObservingOptions.New, context: nil)
         frameAdded = true
      }
   }

   // Stop Key Value Observing Changes
   func ignoreFrameChanges() {

      if(frameAdded) {

         removeObserver(self, forKeyPath: "frame")
         frameAdded = false
      }
   }

   // If the observer adds keypath for "frame", run checkHeight()
   override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {

      if keyPath == "frame" {

         checkHeight()
      }
   }
}

Upvotes: 0

Views: 841

Answers (1)

vadian
vadian

Reputation: 285082

Implement the deinit method and put ignoreFrameChanges() in it

deinit
{
  ignoreFrameChanges()
}

The method is called before the object will be deallocated

Upvotes: 4

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