Android Memory Management for Lifecycle

I am trying to determine how to keep my app safe under various Android lifecycle conditions, such as another app being start, phone going to sleep, etc. I understand the lifecycle states and the event methods I can hook into, but I am 开发者_StackOverflow社区not sure how memory is handled in regard to things I already had references to. I am well aware that my app may be killed at any time if the OS needs to, but what about individual references? Here are a few example scenarios: if my app is running and the user gets a phone call, or the user starts another app, or the phone goes to sleep. Assuming my app did not get killed, can I safely use my references or will I get random null pointers? I guess what this comes down to is... does Android either kill or not kill and app or will it reclaim some memory (where there are still valid references) from an app without killing it?

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Most of the time when the user switches to another app or answers the phone, you app will simply be suspended. When it comes back, onResume() will be called and it will continue on it's way with no issues. References and that kind of thing should be fine. It is recommended that you unregister listeners and re-register them in onResume(), though.

You should always remeber that your app may also be completely killed at any time, so save your data.

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The truth is most of the time the application will not get killed in a brief interruption, for example a call or email, but if you want support these situations you should preform cleanup or saving the data in onPause(). When the application comes back it will execute onResume().

References will not disappear until the activity is destroyed, do not worry about NPE in the pause -> resume scenario unless you are doing something very odd.

If you are using listeners or GPS, you should unregister during onPause() and resume it later.