How come Android can support 2 apps in split screen but not in background?
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)