wulkanowy-mod/app/src/main/res/layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/main_activity_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:baselineAligned="false"
    android:weightSum="1">

    <android.support.design.widget.CoordinatorLayout
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1">

        <android.support.design.widget.AppBarLayout
            android:id="@+id/main_activity_appbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <android.support.v7.widget.Toolbar
                android:id="@+id/main_activity_toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_scrollFlags="scroll|enterAlways" />
        </android.support.design.widget.AppBarLayout>

        <RelativeLayout
            android:id="@+id/main_activity_progress_bar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center">

            <ProgressBar
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:indeterminate="true" />
        </RelativeLayout>

        <com.aurelhubert.ahbottomnavigation.AHBottomNavigationViewPager
            android:id="@+id/main_activity_view_pager"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="@dimen/bottom_navigation_height"
            app:layout_behavior="@string/appbar_scrolling_view_behavior" />

        <com.aurelhubert.ahbottomnavigation.AHBottomNavigation
            android:id="@+id/main_activity_nav"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom" />

    </android.support.design.widget.CoordinatorLayout>
</LinearLayout>