Why handling life-cycle events is important

If you are used to always having control in your applications, you might not understand why all this life-cycle work is necessary. The reason is that in Android, you are not in control of your Activity, the operating system is!

As we have already seen, the Android model is based around activities calling each other. When one Activity calls another, the current Activity is paused at the very least, and may be killed altogether if the system starts to run low on resources. If this happens, your Activity will have to store enough state to come back up later, preferably in the same state it was in when it was killed.

Android has a well-defined life cycle. Life-cycle events can happen even if you are not handing off control to another Activity explicitly. For example, perhaps a call comes in to the handset. If this happens, and your Activity is running, it will be swapped out while the call Activity takes over.