Android tablet navigation bar won't hide

I'm trying to hide the navigation bar, using methods I've found described on the internet.

I have a simple layout which shows a WebView:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="horizontal"
    android:id="@+id/layout" >

    <WebView
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/webview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />

</RelativeLayout>

The code that I'm using at app startup is:

    getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);
    getWindow().addFlags(WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN);
    getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_LOW_PROFILE);
    getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);
    web.setSystemUiVisibility(View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);
    layout.setSystemUiVisibility(View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);

But this doesn't hide the navigation bar.

I've added...

android:theme="@android:style/Theme.NoTitleBar.Fullscreen"

... to my activity too.

How can I achieve this?

You cannot permanently hide the system bar on a tablet.

SYSTEM_UI_FLAG_HIDE_NAVIGATION on Android 4.1 and higher will hide the system bar, but it will reappear as soon as the user does anything.