I set up a detail view, do I have several Nib files that get loaded depending on what item is selected in the root view controller's table.
What I've discovered is that for the Nibs' classes, viewDidUnload is never called, whereas viewWillDisappear is called and dealloc of course is also called.
Anybody know why this would be?
Thanks.
I believe viewDidUnload isn't normally called when a view disappears from view. The reason for this is because dealloc will typically take care of all the memory dumping, so it doesn't need to call viewDidUnload first.
I think an example would help identify when viewDidUnload is called. Let's say you have a UINavigationController and you've pushed on a new view. This new view is very heavy on memory usage, so the app tries to shore up some resources. It does this by seeing if any Views are loaded that aren't currently on the screen. If so, it calls viewDidUnload where ideally you remove things that you built in loadView or viewDidLoad. Then when you go back to that view, it calls loadView or viewDidLoad again to re-build what it dumped off in viewDidUnload.
But if it doesn't need to free up memory to show your detail view, it won't call it in the normal processing of it. That's why viewWillDisappear is called (and dealloc) but never viewDidUnload.
From Apple's documentation:
When a low-memory warning occurs, the UIViewController class purges its views if it knows it can reload or recreate them again later. If this happens, it also calls the viewDidUnload method to give your code a chance to relinquish ownership of any objects that are associated with your view hierarchy, including objects loaded with the nib file, objects created in your viewDidLoad method, and objects created lazily at runtime and added to the view hierarchy. Typically, if your view controller contains outlets (properties or raw variables that contain the IBOutlet keyword), you should use the viewDidUnload method to relinquish ownership of those outlets or any other view-related data that you no longer need.
