memory manager

When a low-memory condition occurs, the system may purge suspended apps without notice to make more space for the foreground app.

The main difference is that instead of your app being made active, it enters the background state to handle the event and then is suspended shortly afterward. When launching into the background, the system still loads your app’s user interface files but it does not display the app’s window.

Event:

Redraw
The view that needs the update
Redraw events do not involve an event object but are simply calls to the view to draw itself. The drawing architecture for iOS is described in Drawing and Printing Guide for iOS.