OK #AndroidDev we need to talk about saving and state in your apps using onSaveInstanceState and friends. Broadly speaking this mechanism is there to have users return to your app after an interruption in using it and carry on where they left off. 1/9
Behind the scenes, the app might have been killed by Android and whatever you've saved in onSavedInstanceState is returned to you to restore the app to the previous state, as if the was app kept running in the background. Smoke and mirrors basically. 2/9
The trick is to save just enough in the Bundle provided in onSavedInstanceState to make sure your app is able to resume where it left off. As a bonus, view state is already saved for you by the system. Saved state is also provided after config changes (like rotation). 3/9
So I'd argue that mosts apps need this at some point somewhere and often I run into apps where not using this mechanism leads to bad UX or even crashes. Worse, often I hear devs say that "an app doesn't get killed that fast" so they do not need to save any state ever. 4/9
The thing is that you don't know. While it might not be killed "that fast" on your high end developer phone there's absolutely no guarantee that it isn't killed fast when the user isn't interacting with your app. Hello Nexus 5X user here 👋 5/9
Another argument is that "when the user comes back after ages" it doesn't make sense to restore state. Well, again, if I use your app, get a phone call, check something on Google Maps, then return, your app might have already be killed. You just don't know! 6/9
Lately some of the more clever excuses are more like "We use ViewModel and it keeps state on rotation so we don't need to bother with onSaveInstanceState". That's great 🙌 ...as long as your process is alive. ☠️ 7/9
ViewModel is great and it helps with state and things like network calls that need to keep going regardless of a configuration change, but you still need something to restore the state of your ViewModel when the app is restarted by the OS. 8/9
So start by implementing onSaveInstanceState, and once you have that sorted you are in a great starting position for restoring your ViewModel state too. Test this stuff by turning the "Don't keep activities" developer option to see if weird stuff happens. 9/9
