3

I'm dealing with some deallocation issue and perhaps strong or circular referencing that can't figure out. I have three UIViews instantiating like below:

There is one main ViewController which I have added a UIView inside it in storyboard and the UIView has a weak outlet inside the class like: 

class ViewController : UIViewController {

    //MARK: - outlets
    @IBOutlet weak var firstView: FirstUiview!

}

second UIView is added as a subview to the first view programmatically like: 

class FirstUiview : UIView { 

        //creating an instance of secondUiView 
        lazy var mySecondView: SecondViewClass = {
          let dv = SecondViewClass()
          dv.backgroundColor = UIColor.red
          return dv
        }()


        //sometime later by clicking on a button 
        self.addSubview(mySecondView)

        //a button will be tapped to remove mySecondView; 
        //later will be called at some point upon tapping:

       func removingSecondViewByTapping()  {
         if mySecondView.isDescendant(of: self) {
           mySecondView.removeFromSuperview()
        }
       }

}

Now the SecondViewClass is : 

class SecondViewClass : UIView { 

      //in this class I create bunch of uiview objects like below: 
      lazy var aView : UIView = {
        let hl = UIView()
        hl.tag = 0
        hl.backgroundColor = UIColor.lightGray
        return hl
      }()

      self.addSubview(aView) //... this goes on and I add other similar views the same way.

        //creating an instance of thirdView
        var let thirdView = UIView() 
        self.addSubview(thirdView)

}

Now if user taps the button to remove mySecondView and then add it again at some other time (still in the same ViewController) I expect all the subviews of mySecondView to have been released and gone but they are all there. I would appreciate it a lot if someone can point it to me where am I keeping a strong reference or if there is a circular referencing issue? or perhaps something else?

Rob
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TheBen
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  • Why would you expect the 2nd view's subviews to be gone? Removing `mySecondView` from its superview doesn't make it remove all its subviews from itself. – dan Oct 27 '16 at 19:47
  • @dan Oh wait, I thought view.removeFromSuperview will release and destroy the view including its subviews unless its subviews have references to something that is held, will it not? if not , couldn't you guide me on how I can totally remove the sending view including it's subviews? – TheBen Oct 27 '16 at 19:55

1 Answers1

5

You have two strong references to your views, your custom property and the view hierarchy reference established when you call addSubview. When you remove the view from the view hierarchy, your class, itself, still has its strong reference to it.

You could solve this by making your reference optional, and when you call removeFromSuperview, also manually set your reference to nil. Or, perhaps easier, you might resolve this by using weak references, letting the view hierarchy maintain the strong references for you. And because your custom property is weak, when you remove it from the view hierarchy (thus eliminating the only strong reference to it), your weak reference will automatically become nil:

class FirstView: UIView {

    weak var secondView: SecondView?       // note the `weak` reference, which is obviously an optional

    //sometime later by clicking on a button

    func doSomething() {
        let subview = SecondView()
        subview.backgroundColor = .red
        self.addSubview(subview)
        secondView = subview
    }

    // a button will be tapped to remove secondView;
    // later will be called at some point upon tapping ...

    func removingSecondViewByTapping()  {
        secondView?.removeFromSuperview()
    }
}
Rob
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  • Thanks for your reply. It sure does look like the right explanation and answer. I'm afraid that the issue is deeper than that for me as I tried to simplify it here. Very clear answer though! I tried this with no lock yet. My third view has a protocol that the parent view conforms to it, could that be another issue? I have made sure that it's a weak protocol delegate, i.e, something like http://stackoverflow.com/a/24104371/5601401 – TheBen Oct 27 '16 at 23:51
  • Yes, failure to use weak protocols could also be a problem. So, if you've fixed the above and have also made sure to use `weak` delegate references, and you're still not seeing your views deallocated, you need to diagnose what's keeping the strong reference. Using the "Debug Memory Graph" (see http://stackoverflow.com/a/30993476/1271826) can be useful in tracking down any additional problems you might have. – Rob Oct 28 '16 at 01:01
  • "Fatal error: Unexpectedly found nil while unwrapping an Optional value" on the first line that executes after initialization of object set as `weak`. Every time. – Brandon A Sep 05 '18 at 20:21
  • @BrandonA - If you notice, above, I set the view to be a local variable, add that to be a subview (which establishes a strong relationship) and only then do I set that `weak` ivar. If you try to shortcut that and not use the local variable, or if you don’t add it to the view hierarchy before you leave the function, you can get an error like what you describe. I’d suggest you create a [gist](http://gist.github.com), showing us what you tried. But the above is a tried-and-true technique. – Rob Sep 05 '18 at 21:09