I have a scenario where I have:
- a UINavigationController with a UIViewController (mainVC) with a UIView (mainView) containing a UIScrollView (scrollView)
- a fullscreen button in the mainView, where upon tapping on it pushes a new UIViewController (fullScreenVC), with scrollView object passed by reference to it (stored with the property attributes nonatomic and assign). fullScreenVC shows the scrollView object correctly.
- upon closing fullScreenVC, a NSNotification is sent to mainVC. Here lies the problem…
When fullScreenVC is removed, scrollView is no longer shown in mainVC. I can tell it still exists though, through printing out scrollView on the logs during the notification.
I would of thought that by sending and storing scrollView by reference, mainVC would still have it retained. I also tried sending scrollView back to mainVC in case it was removed, but that didn’t do anything.
The only way of solving it was to add scrollView back into mainVC on the notification step. Is there something special I have to do when sending UIScrollView objects around (or more generally UIKit objects)? Or did I do something stupid somewhere?
There is no pass-by-reference. In Objective-C, we have pointers to objects, and those pointers are assigned and passed around (never the objects themselves).
Anyway, that is not relevant here. Your issue is that in UIKit, a view can only have one superview (it is a tree hierarchy). When you add a view as a subview to another view, it is automatically removed from its previous superview, if there was one. See the documentation for addSubview: here: https://developer.apple.com/library/ios/#documentation/uikit/reference/UIView_Class/UIView/UIView.html#//apple_ref/occ/instm/UIView/addSubview:
Do you really need to show the same scroll view in two different screens? It seems kind of odd. You should either have two different scroll views; or, you can make sure to add it back to your “mainView” after you are done with the other one.