iOS app life cycle

We can categorized iOS life cycle mainly in two category:

1) The App launch cycle
2) View Controller life cycle

The launch cycle states different app states in which an iOS app can transit in its life . The different app states are as:

1) Not running
2) Inactive
3) Active
4) Background
5) Suspended

When an app goes from one states to another it is called app delegate methods. These methods provides a way  to take appropriate action  on app state changes. These methods are as:

application:didFinishLaunchingWithOption: called when app launches first time.

applicationDidBecomeActive: called after app enters in foreground.

applicationWillResignActive: called before an app enters in background.

applicationDidEnterBackground: called after app enters in background. In this state an app may be suspended at any time.

applicationWillEnterForeground:called when app changes state from background to foreground. But app is not yet active

applicationWillTerminated: This method is not called when an app is suspended or user terminated the app explicitly.


View Controller life cycle:

viewDidLoad: called only once  during initial load of the interface.

viewWillAppear:This method is called just  before views appears or renders on screen every time when you   navigate or switch between different views.

viewDidAppear: called when views completely.  Here we can handle UI or functionalities.

viewWillDisappear: called before view is removed or any animation is configured.

viewDidDisappear:called when view is removed.