How does UINavigationController keep track of multiple UIViewControllers?

I have developed an application that uses UINavigationController to handle multiple instances of the same UIViewController, and it is working great. The UIViewControllers that I am using, however, are using a lot of images in a sometimes very big UITableView as loaded from the server, so I am beginning to be more conscience of performance and memory.

What happens to a UIViewController that isn't at the top of the stack? If I drill down through a few views, that all have images, whenever I return to the view, the UINavigationController presents the view without any loading开发者_StackOverflow, so I'm wondering if those views on the stack are in any way potentially hogging lots of valuable resources? Such as memory?

What is the best way to handle that situation? Is there anything I should know about that I apparently don't?

Thanks!

This is, actually, explained in the documentation for iOS. Check XCode>Organiser>Documentation>iOS, there is a nice drawing explaining how the UINavigationController stack works, that should be better than words.

However, in a nutshell, you have viewDidLoad and viewWillAppear (and their opposites) methods that serve to alleviate your fears. They should be used to create/delete any "memory hogging" parts of your code that you don't need "right now". However, as far as I know, you don't have control over what iOS will decide is necessary to flush or not, if it's controlled directly by UINavigationController.