iOS Programming: The Big Nerd Ranch Guide

24 State Restoration

As we discussed in Chapter 18, applications have limited life spans. If iOS ever needs more memory and your application is in the background, Apple might kill it to return memory to the system. This should be transparent to your users; they should always return to the last spot they were within the application.

To achieve this transparency, you must adopt state restoration within your application. State restoration works a lot like another technology you have used to persist data – archiving. When the application is suspended, a snapshot of the view controller hierarchy is saved. If the application was killed before the user opens it again, its state will be restored upon launch. (If the application has not ...