Explain the stages of life and the main methods of UIViewController at different stages of its existence.

The lifecycle of a UIViewController consists of several stages, each accompanied by calls to specific methods:

1. Initialization and loading the view:

   • init(coder:) or init(nibName:bundle:) — controller initialization.
   • loadView() — creates and initializes the controller's root view (usually not overridden if using storyboard).
   • viewDidLoad() — called after the view is loaded into memory; typically used for initial UI setup and data initialization.

2. View appearance on screen:

   • viewWillAppear(_:) — called before the view appears on the screen; UI can be updated.
   • viewDidAppear(_:) — called after the view appears; animations or data loading can be started here.

3. View disappearance:

   • viewWillDisappear(_:) — called before the view disappears; state can be saved or operations canceled.
   • viewDidDisappear(_:) — called after the view disappears; resources are released, timers are stopped.

4. Memory management:

   • didReceiveMemoryWarning() — called when there is a memory warning; unnecessary resources should be released here.

5. Controller removal:

   • deinit — destructor, called when the controller is deallocated from memory.

These methods help manage the controller's state and its view at different stages of the lifecycle, ensuring proper interface operation and efficient resource use.