ios应运程序的五种状态

Not running

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

Inactive

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.

Active

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

Background

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

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.