How come Android can support 2 apps in split screen but not in background? I read another question on Ask Different about why apps have to reload when you switch to another app and back, and I think it's the same for Android.

But why does this not happen in split screen?

For instance, when I'm using a ressource-consuming app (pokémon Go for example), of I switch to another app (let's say Whatsapp) and stay a little too long on it, the system will kill other apps (possibly the most consuming first), and when I come back to the game I'll have to face the (long) loading again.

However, I can split the screen while playing, having the game on one half and any other app on the other. 


Why is it so different? If the system is capable of running Youtube and Pokémon Go at the same time, why does it kill Pokémon Go if I do a single search on the youtube app when not split?
If the system "locks" Pokémon Go and kills other apps when in split screen, is there no way for me to "lock" it too in normal mode?
On Android, only 1 app can be in the active (or &quot;resumed&quot;) state, but when the app is still visible but not currently the active app, it will be in the paused state.
So when you use multi window, the app you've interacted with last will be the active app, while the other app is paused.
If the app is no longer visible, it will enter the stopped state. In the stopped state, the elements on the screen will still be kept in memory, but if other apps require more memory the app might get killed, destroying the data causing the screen to reload when you come back to it.
If you'd like to learn more, there's a guide to understanding the activity lifecycle here. (An Activity is just a single page in the app)