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1.For each view controller you choose to preserve, you also need to decide on how you want to restore it later. UIKit offers two ways to recreate objects. You can let your app delegate recreate it or you can assign a restoration class to the view controller and let that class recreate it. A restoration classimplements the UIViewControllerRestoration protocol and is responsible for finding or creating a designated object at restore time. Here are some tips for when to use each one: