1. It is recommended that users install Fulscrn, https://play.google.com/store/apps/details?id=me.dt2dev.fullscreen.free, the above is soft advertising, but it is really effective

2. https://developer.android.com/training/system-ui/immersive.html This should be what you need

Immersive Mode only supports Kitkat and Lollipop, ICS and above can use SYSTEM_UI_FLAG_LOW_PROFILE

if (Build.VERSION.SDK_INT >= 19) {

getWindow().getDecorView().setSystemUiVisibility(
        View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY);

} else {

if (Build.VERSION.SDK_INT > 10) {
    findViewById(android.R.id.content).setSystemUiVisibility(View.SYSTEM_UI_FLAG_VISIBLE);
    getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_LOW_PROFILE);
}

}