Question

I have a simple Tab bar navigation app

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[ Tab 1 ]_[ Tab 2 ]

When Tab 1 is touched, Screen 1 is shown. When Tab 2 is pressed, Screen 2 is shown.

How can I call an action each time a screen is shown (not just on the viewDidLoad event).

Do I have to listen to the touch event on the Tab bar or is there an event in the ViewController I can listen for?

Answer 1

viewDidLoad gets called when the nib is being loaded into memory. When a view is actually appearing on the screen, viewDidAppear gets called.

[Edit]

This is the (natural) order of callbacks:
initWithNibName:Bundle: -> awakeFromNib -> loadView -> viewDidLoad -> viewWillAppear -> viewDidAppear

[Edit2]

see here for an excellent explanation: https://stackoverflow.com/a/5109277/347353