How to show some content when android app in onStop

Question

I have a simple question: is there a way to show something, like a progress bar, when the app is onStop? Because my app does a lot of computation, and when it is actually doing that goes on onStop and a black screen is showed, finally when the computation is done it return to the normal screen. So, it is all correct in a functional point of view, but aesthetically it is not so good. Have you got any tip?

Answer 1

So you basically want to prevent your device from going to sleep while the computation is running? That is called a WakeLock, and it basically prevents your activity from turning off the screen. Be careful to use it sparingly, to avoid draining your users battery.

It's very easy to do this programatically:

class MainActivity : Activity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        window.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
    }
}

Or you can add an xml attribute to the view you want to show:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:keepScreenOn="true">
    ...
</RelativeLayout>

For more information and details have a look at the documentation