In iOS development, understanding the app lifecycle and its various states is crucial for creating efficient and responsive applications. An iOS app can exist in several states, each representing a different phase of its lifecycle. Here are the primary states an iOS app can be in:
1. Not Running
The "Not Running" state is when the app is not executing any code. This occurs either because the app has not been launched yet or because it was running but has been terminated by the system or the user[1][2][4].
2. Inactive
An app enters the "Inactive" state when it is in the foreground but not receiving events. This typically happens during transitions, such as when the app is launching or about to move to the background. For example, an app might be inactive when a phone call comes in or when the user is switching between apps[1][2][5].
3. Active
The "Active" state is when the app is running in the foreground and receiving events. This is the normal operational state for an app when it is in use. In this state, the app is fully interactive and can respond to user inputs[1][2][4].
4. Background
An app is in the "Background" state when it is still executing code but is not visible on the screen. This can happen when the user switches to another app. In this state, the app can perform tasks such as downloading data or playing audio. However, the system may limit the amount of time an app can spend in this state before moving it to the suspended state[1][2][5].
5. Suspended
In the "Suspended" state, the app is in memory but is not executing any code. The system moves apps to this state to free up resources for other apps. While suspended, the app remains in memory and can be quickly resumed if the user returns to it. However, the system can purge suspended apps from memory if resources are low[1][2][4].
6. Terminated
Although not always listed as a separate state, "Terminated" refers to when an app has been completely removed from memory. This can occur when the user manually quits the app or when the system terminates it to free up resources. When an app is terminated, it returns to the "Not Running" state[1].
State Transitions
Understanding the transitions between these states is also important. For instance:
