pda-web/app/src/main/res/layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <WebView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/webView" />

    <ProgressBar
            android:id="@+id/loading"
            android:layout_gravity="center"
            android:layout_width="wrap_content"
            android:visibility="invisible"
            android:layout_height="wrap_content" />

</FrameLayout>