how do "saved states" work? (Android)

Question

I just read a pretty interesting article on how android (and i assume other OSs) work when low on memory. How is this done theoretically? Is it similar to Java's object serialization?

Answer 1

In a word: yes.

In a few more words, sort of. You have to handle more of it manually than personally I'd like. Essentially, all Android provides for you is a hash to shove a few serializable objects, referenced by strings, that is guaranteed to be safe across application shutdowns. So, whenever something happens that you'd like to preserve across a shutdown of your application, you are responsible for updating this saved state hash (and letting Android know that you've done so). This includes things like half-finished text entry in form fields. That means you have a lot to listen to.

Android will then call a particular hook in your Activity that handles restoring state to the Activity when it recycles your application and you need to do so. This doesn't happen for all recycles — there are various states of being/existence for your application.

The screwy part is that because you're expected to do this sort of tedious work anyway, Android gets lazy and implements things like screen rotation as a full recycle of your application.

I'm making it sound worse than it really is once you get used to it; it's really not a bad way of solving the problem in the confines of Java and mobile computing.

Of course, this is a response regarding Android. Other (desktop) OS's rely on Virtual Memory and Paging to deal with memory constraints.