When the activity enters or exits picture-in-picture mode the system calls Activity.onPictureInPictureModeChanged() or Fragment.onPictureInPictureModeChanged().

You can implement your code inside this:

 override fun onPictureInPictureModeChanged(isInPictureInPictureMode: Boolean,
                                           newConfig: Configuration) {
    if (isInPictureInPictureMode) {
        // Hide the full-screen UI (controls, etc.) while in picture-in-picture mode.
    } else {
        // Restore the full-screen UI.
    }
}

We are using the calls page with a picture in picture(pip) feature.

Problem :
In case user dismiss the pip popup window (by drag down to dismiss) we not able to detect that.

How to detect picture in picture window drag down to dismiss?

Update:
Set picture in picture

// RemoteRenderLayout -> call preview layout. You can set anyone view
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {

    Rational aspectRatio = new Rational(
        remoteRenderLayout.getWidth(), remoteRenderLayout.getHeight());
    PictureInPictureParams params = new PictureInPictureParams.Builder()
        .setAspectRatio(aspectRatio)
        .build();
    enterPictureInPictureMode(params);
}
else{

    enterPictureInPictureMode();
}