CODEWITHSUNDEEP
ios
user1099123
user1099123

Reputation: 6683

Is it possible that a weak reference might be garbage collected while I am using its parent in IOS?

Say I have a parent UIView. This UIView has a weak pointer to a subview UIImageView. If UIView is currently displayed on the screen, is it possible for the image view to be garbage collected since the parent UIview only has a weak reference to the UIImageView?

FYI UIview and UIImageView would both be on the screen

Upvotes: 3

Views: 163

Answers (4)

Rob
Rob

Reputation: 437692

When you add a subview to your view, it will, by definition, maintain a strong reference to that subview. That's just part of the addSubview internal process of maintaining view hierarchies. The view will keep this strong reference to its subviews until that subview is manually removed (e.g., via removeFromSuperview) or if the superview, itself, is removed (e.g. you dismissed its view controller).

These strong references that views internally maintain on their subviews should not be confused with the weak references that you (or IB) might add to your view or view controller subclass .h file. Those weak references are just providing you a convenient way of referencing the subview or control. The fact that your .h file has a weak reference to the the subview, such as an IBOutlet for your benefit, doesn't alter the fact that views automatically already have a strong reference to their subviews behind the scenes as part of the overall view hierarchy.

So, a subview, such as an image view will only get deallocated when its last strong reference is removed (or in non-ARC language, when the retain count falls to zero). If you've added the image view as a subview, it won't get deallocated until that strong reference is eliminated (i.e. the image view is removed from it's superview, or the superview, itself is removed). Obviously, if you're maintaining other strong references to the control, those would have to be removed, as well, for the subview to be released.

A caveat: If you're not using ARC, i.e., you're doing manual reference counting (e.g. manually calling release and autorelease), it's certainly possible for you to make a programming mistake and "over release" the image view, thereby letting the retain count fall to zero, and thus allowing it to be deallocated prematurely. But given that you're referencing weak properties in your question, you must be using ARC, so this observation is moot.

There are other situations in which sloppy use of weak variables can cause problems, but I hesitate to elaborate unless you tell us that the subview is not showing up at all.

(By the way, you mention garbage collection (GC) in your question, but I assume the real question was "is it possible that my subview might be deallocated while ...". Obviously, iOS doesn't have GC. But I assume the real question is whether your subview might be deallocated while it's still present on its superview.)

Upvotes: 1

matt
matt

Reputation: 535325

This UIView has a weak pointer to a subview UIImageView

Stop. If the UIImageView is a subview of the UIView, then the UIView has a strong pointer to the UIImageView. End of story.

In other words, a view retains its subviews. As long as the subview is a subview, it cannot vanish in a puff of smoke.

Now, on the other hand, if you remove that subview, then you have to worry about its memory management or it might vanish in a puff of smoke.

Upvotes: 4

Vinzzz
Vinzzz

Reputation: 11724

You use 'weak' property on subviews when they're expected to be created and directly added to a view subviews hierarchy : UIView addSubview: already keeps a strong reference to the view.

if your view is a weak property of a UIViewController, you typically create if from NIB, or in -(void)viewDidLoad. If the controller's view is discarded because not needed anymore, your subview will be too.

Upvotes: 1

rooster117
rooster117

Reputation: 5552

If the UIVIew has the UIImageView added to it the reference will be incremented by that action wouldn't be released until it was removed from the view.

Without knowing why you asked this I would also say that I don't think there would be any harm in having a string reference to it because at the point where the UIView is cleaned up it would also dereference the the uiimageview and it would be released then.

Also I know you said garbage collected but iOS doesn't have garbage collection. I know what you mean though

Upvotes: 0

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