Android – footer scrolls off screen when used in CoordinatorLayout

I use a simplified version of Learn OpenGL ES’s solution (https://stackoverflow.com/a/33396965/778951) — which improves on Noa’s solution (https://stackoverflow.com/a/31140112/1317564). It works fine for my simple quick-return toolbar above a TabLayout with footer buttons in each tab’s ViewPager content.

Just set the FixScrollingFooterBehavior as the layout_behavior on the View/ViewGroup you want to keep aligned at the bottom of the screen.

Layout:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

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

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?android:attr/actionBarSize"
                android:minHeight="?android:attr/actionBarSize"
                app:title="Foo"
                app:layout_scrollFlags="scroll|enterAlways|snap"
                />

            <android.support.design.widget.TabLayout
                android:id="@+id/tabs"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:tabMode="fixed"/>

    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="com.spreeza.shop.ui.widgets.FixScrollingFooterBehavior"
        />

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

Behavior:

public class FixScrollingFooterBehavior extends AppBarLayout.ScrollingViewBehavior {

    private AppBarLayout appBarLayout;

    public FixScrollingFooterBehavior() {
        super();
    }

    public FixScrollingFooterBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean onDependentViewChanged(CoordinatorLayout parent, View child, View dependency) {

        if (appBarLayout == null) {
            appBarLayout = (AppBarLayout) dependency;
        }

        final boolean result = super.onDependentViewChanged(parent, child, dependency);
        final int bottomPadding = calculateBottomPadding(appBarLayout);
        final boolean paddingChanged = bottomPadding != child.getPaddingBottom();
        if (paddingChanged) {
            child.setPadding(
                child.getPaddingLeft(),
                child.getPaddingTop(),
                child.getPaddingRight(),
                bottomPadding);
            child.requestLayout();
        }
        return paddingChanged || result;
    }


    // Calculate the padding needed to keep the bottom of the view pager's content at the same location on the screen.
    private int calculateBottomPadding(AppBarLayout dependency) {
        final int totalScrollRange = dependency.getTotalScrollRange();
        return totalScrollRange + dependency.getTop();
    }
}