When should I release objects in -(void)viewDidUnload rather than in -dealloc?

cocoa-touch, ios, iphone, memory-management, objective-c

Solution

In addition to what has already been indicated, I wanted to elaborate more about logic behind `-viewDidUnload`.

One of the most important reasons for implementing it is that `UIViewController` subclasses commonly also contain owning references to various subviews in the view hierarchy. These properties could have been set through `IBOutlets` when loading from a nib, or programmatically inside `-loadView`, for instance.

The additional ownership of subviews by the `UIViewController` means that even when its view is removed from the view hierarchy and released to save memory, through which the subviews are also released by the view, they will not actually be deallocated because the `UIViewController` itself still contains its own outstanding retaining references to those objects as well. Releasing the `UIViewController` additional ownership of these objects ensures they will be deallocated as well to free memory.

The objects that you release here are usually recreated and set again when the `UIViewController` view is `re-loaded`, either from a Nib or through an implementation of `-loadView`.

Also note that the `UIViewController` `view` property is `nil` by the time this method is called.

Problem

Original source