Controversy with ownership in Objective C

Question

During the last time I'm trying to become aware of Objective-C memory management and once I asked myself the following question:

Sinceweak reference in Objective-C let us to avoid retain cycles why not to use them all the time?

Answer 1

Sinceweak reference in Objective-C let us to avoid retain cycles why not to use them all the time?

Because an object is deallocated as soon as there are no strong references to it.

More importantly, a strong reference is often wanted in order to prevent an object's deallocation. For example, a view controller is ultimately responsible for its view -- it wouldn't make much sense to have the controller's view suddenly just disappear. So UIViewController's view property is strong.

A retain cycle happens when two objects each have strong references to the other. Neither object can be deallocated as long as the other one keeps it's strong reference. This isn't really a problem if you're aware of the situation, because you can break the retain cycle by eliminating either of the references. However, it's easy to not be aware of the cycle, or to forget to deal with it, and then you've got two objects keeping each other in memory beyond their useful lifetime. Making one of those references weak eliminates the problem, but it also means that the referenced object may be deallocated and the reference may become nil at any point. In practice, that's usually not a problem.

Answer 2

An object only stays in memory while there is at least one strong (default) reference to it. If you only use weak references, the object is immediately deallocated.

Simply said, "weak" means: This object belongs to someone else, I'm only accessing it and I don't mind if it disappears.