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 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?
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.