iOS doesn't report when an app will be suspended (placed from background into a non-processing state) nor does it seem to fire a notification once the app has resumed. There is some confusion about this as there is a notification when the app becomes "active" or will resign the "active" state, however this is not always the right value needed. iOS Apps have a number of states:
- Active: App is in the foreground (frontmost) and there are no notifications or menu's pulled over it. Pulling a menu down or getting an external notification or text message will cause the app to "resign" active, and resume active once the alert has been dealt with.
- Background: App is not in the foreground but still processing. This happens briefly before suspend if there are no background tasks running, or can be a permanent state if there is a long running background mode (audio, location, etc) running.