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Editorial Team
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Asked: 2026-06-06T05:38:07+00:00

I have an app which is based on a UINavigationController . There is a

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I have an app which is based on a UINavigationController. There is a menu screen with buttons that segue (push onto navigation controller stack) to one of 9 other “sub-screens”. None of these sub-screens segue to any other screen. When a user is done inputing data on a “sub-screen” they can press a done button which will pop back to the original menu screen. (If you’re having difficulty picturing this, imagine a tree like storyboard where there is one root ViewController and then 9 leaf viewControllers).

Ok, so with that setup I have a few questions about how viewDidLoad works.

~ First, is viewDidLoad supposed to be called every time we transition to a sub-screen. For example, suppose I go from the menu screen to sub-screen “B”, back to the menu screen and then back to sub-screen “B”. Should B’s viewDidLoad method be called twice? If not, why might mine be getting called twice?

~ Second, assuming that it will get called each time, what do I do if I have a lot of long operations that need to be performed exactly one time for each sub-screen? Where should I put them (if I put them in viewDidLoad it would happen multiple times if the user kept going back and forth between this page and the menu)?

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1 Answer

  1. Editorial Team

    To answer your questions:

    1. Yes, in general B’s viewDidLoad method should be called each time that it is pushed onto the UINavigationController’s stack. This is because each time that B is popped off of the stack it is typically released, and each time that you go to B a new instance of B is created.

    2. There could be numerous ways to handle this type of situation. It is hard to tell what is right for you without seeing exactly what you are trying to do. One way would be to create a singleton object that handles the processing. The reason this might be better than handling it within your UIViewController is that a singleton can live throughout the lifetime of the application, whereas UIViewControllers typically have a relatively short lifespan. Singleton objects can be created just once and they can manage whatever operations and data that you need to persist through the lifetime of your application.

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