iOS Application Lifecycle

Why do we need to know
Firstly, we should respond properly to the launch of the app. Some third-party libraries need set up in different states of the app. Also, we should prepare the app to work in the foreground. We might need to provide a different user experience. For instance, our app can require a password whenever it goes to the foreground. On the other hand, our app can upload images while the app is in the background like Dropbox does. Even we might want to reopen from where the user left after the termination of the app. So, each feature requires different implementations in different app states. So, it can be critical to know the states and the transitions while providing a different and better user experience.

Application lifecycle

Not Running:
The app is not launched or terminated by the system.

Background:
App is in the background and still able to run code. But the duration of this state is determined by the OS and code execution can be interrupted at any time. If the developer requests extra time to execute some code, the period can be longer. There are some situations in which the app can be launched directly into the background mode. For example, the app can start in background mode if the app starts downloading some content when the remote push notification is received.

Foreground
Inactive:
It’s generally a transition state between active and background state to launch of the app. For example, if we receive a phone call when the app is in the foreground, it goes into an inactive state.

Active:
The app is in the active state when it is in the foreground and it’s able to receive events.

Suspended:
When the app is in the background state, the system suspends it and the app cannot execute any code. There isn’t any notification for the suspending event. The system automatically suspends the app.