iOS Application States Quetions

1) Why an app on iOS device behaves differently when running in foreground than in background?
  An application behaves differently when running in foreground than in background because of the limitation of resources on iOS devices.
2)Which framework delivers event to custom object when app is in foreground?

The UIKit infrastructure takes care of delivering events to custom objects. As an app developer, you have to override methods in the appropriate objects to process those events.

3)When an app is said to be in not running state?
An app is said to be in 'not running' state when:
- it is not launched.
- it gets terminated by the system during running.

4)Assume that your app is running in the foreground but is currently not receiving events. In which sate it would be in?
An app will be in InActive state if it is running in the foreground but is currently not receiving events. An app stays in InActive state only briefly as it transitions to a different state.

5)Give example scenarios when an application goes into InActive state?
An app can get into InActive state when the user locks the screen or the system prompts the user to respond to some event e.g. SMS message, incoming call etc.

6)When an app is said to be in active state?
An app is said to be in active state when it is running in foreground and is receiving events.

7)Name the app sate which it reaches briefly on its way to being suspended.
An app enters background state briefly on its way to being suspended.

8)Assume that an app is not in foreground but is still executing code. In which state will it be in?
Background state.

9)An app is loaded into memory but is not executing any code. In which state will it be in?
An app is said to be in suspended state when it is still in memory but is not executing any code.

10)Assume that system is running low on memory. What can system do for suspended apps?
In case system is running low on memory, the system may purge suspended apps without notice.

11)How can you respond to state transitions on your app?
On state transitions can be responded to state changes in an appropriate way by calling corresponding methods on app's delegate object.

For example:
applicationDidBecomeActive method can be used to prepare to run as the foreground app.
applicationDidEnterBackground method can be used to execute some code when app is running in the background and may be suspended at any time.
applicationWillEnterForeground method can be used to execute some code when your app is moving out of the background
applicationWillTerminate method is called when your app is being terminated.

12) List down app's state transitions when it gets launched?
Before the launch of an app, it is said to be in not running state.
When an app is launched, it moves to the active or background state, after transitioning briefly through the inactive state.
13)What are the App states? Explain them?

Not running State:  The app has not been launched or was running but was terminated by the system.

Inactive state: The app is running in the foreground but is currently not receiving events. (It may be executing other code though.) An app usually stays in this state only briefly as it transitions to a different state. The only time it stays inactive for any period of time is when the user locks the screen or the system prompts the user to respond to some event, such as an incoming phone call or SMS message.

Active state: The app is running in the foreground and is receiving events. This is the normal mode for foreground apps.

Background state:  The app is in the background and executing code. Most apps enter this state briefly on their way to being suspended. However, an app that requests extra execution time may remain in this state for a period of time. In addition, an app being launched directly into the background enters this state instead of the inactive state. For information about how to execute code while in the background, see “Background Execution and Multitasking.”

Suspended state: The app is in the background but is not executing code. The system moves apps to this state automatically and does not notify them before doing so. While suspended, an app remains in memory but does not execute any code. When a low-memory condition occurs, the system may purge suspended apps without notice to make more space for the foreground app.