UIViewController Lifecycle

A small cheat sheet on the UIViewController lifecycle - which methods are called, and in what order, during different transitions between UIViewControllers.

Controller A Pushes to Controller B

Call order during the transition:

1. initWithCoder:
   1. When a storyboard is used, this method is called instead of init or initWithNibName:bundle:
2. awakeFromNib
3. willMoveToParentViewController:
4. prefersStatusBarHidden
5. preferredStatusBarUpdateAnimation
6. loadView
   1. loadView assigns all outlets (IBOutlets) to the corresponding @property.
7. prepareForSegue:sender:
8. viewDidLoad
   1. All outlets are already connected, but the views have not been rendered yet
9. extendedLayoutIncludesOpaqueBars
10. edgesForExtendedLayout
11. viewWillAppear:
12. extendedLayoutIncludesOpaqueBars
13. edgesForExtendedLayout
14. updateViewConstraints
15. viewWillLayoutSubviews
16. viewDidLayoutSubviews
17. Animation
18. viewDidAppear:
19. didMoveToParentViewController:
20. updateViewConstraints
21. viewWillLayoutSubviews
22. viewDidLayoutSubviews

Some of the methods are called more than once. Layout is called twice - before and after the animation.

Controller B Pushes to Controller C

During the transition:

1. prepareForSegue:sender:
2. viewWillDisappear:
3. updateViewConstraints
4. Animation
5. viewDidDisappear:

Controller C Pops to Controller B

When returning from C to B, this happens:

1. prefersStatusBarHidden
2. preferredStatusBarUpdateAnimation
3. extendedLayoutIncludesOpaqueBars
4. edgesForExtendedLayout
5. viewWillAppear:
6. extendedLayoutIncludesOpaqueBars
7. edgesForExtendedLayout
8. updateViewConstraints
9. viewWillLayoutSubviews
10. viewDidLayoutSubviews
11. Animation
12. viewDidAppear:
13. updateViewConstraints
14. viewWillLayoutSubviews
15. viewDidLayoutSubviews

Controller B Pops to Controller A

Leaving B for good:

1. willMoveToParentViewController:
   1. The argument for this call is nil, which means that scene B will be removed from the hierarchy.
2. viewWillDisappear:
3. updateViewConstraints
4. viewDidDisappear:
5. Animation
6. didMoveToParentViewController:
   1. The argument is also nil
7. dealloc

Source.