UIApplication and agents

All mobile operating systems have a fatal disadvantage: apps are vulnerable to interruptions. For example, a call or lock screen will cause the app to enter the background or even be terminated there are many other similar situations that can cause the app to be disturbed, and when the app is disturbed, there will be some system events, UIApplication will notify its delegate object, Let the delegate agent handle these system events? The delegate can handle events such as: 1. Application lifecycle events (such as program startup and shutdown) 2. System events (such as incoming calls) 3. Memory Warning 4 ...