 class PopoverViewController: NSViewController
 {
     @IBOutlet var addButton: NSButton!
-    var targetViews: NSMutableArray?
-    
+    var targetViews: Array<TargetView>?
     
     override func viewDidLoad()
     {
         super.viewDidLoad()
-        self.targetViews = NSMutableArray()
+        self.targetViews = Array()
     }
     
     func shouldAddTarget() -> Bool

        self.view.addSubview(targetView)
        targetView.removeButton.target = self
        targetView.removeButton.action = Selector("removeTargetView:")
        self.targetViews?.addObject(targetView)
        self.arrangeTargetViews()
        self.addButton.enabled = self.shouldAddTarget()
    }

    {
        for var i = self.targetViews!.count - 1; i >= 0; i--
        {
            let targetView = self.targetViews![i] as TargetView
            
            targetView.snp_remakeConstraints { (make) -> Void in
                let upperView: NSView!
