ViewCenteringBehavior.java

import android.content.Context;
import android.support.annotation.Keep;
import android.support.annotation.Nullable;
import android.support.design.widget.AppBarLayout;
import android.support.design.widget.CoordinatorLayout;
import android.support.v4.view.ViewCompat;
import android.util.AttributeSet;
import android.view.View;

@Keep
public class ViewCenteringBehavior extends CoordinatorLayout.Behavior<View> {
    public ViewCenteringBehavior() {
    }

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

    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent, View child, View dependency) {
        return dependency instanceof AppBarLayout;
    }

    @Override
    public boolean onDependentViewChanged(CoordinatorLayout parent, View child, View dependency) {
        return updateViewPosition(parent, child, (AppBarLayout) dependency);
    }

    @Override
    public boolean onLayoutChild(CoordinatorLayout parent, View child, int layoutDirection) {
        parent.onLayoutChild(child, layoutDirection);

        AppBarLayout appBarLayout = null;

        for (View dependency : parent.getDependencies(child)) {
            if (dependency instanceof AppBarLayout) {
                appBarLayout = (AppBarLayout) dependency;
                break;
            }
        }

        updateViewPosition(parent, child, appBarLayout);
        return true;
    }

    private boolean updateViewPosition(CoordinatorLayout parent, View child, @Nullable AppBarLayout appBarLayout) {
        final int top = appBarLayout != null ? appBarLayout.getBottom() : 0;
        final int topOffset = (top + parent.getBottom() - child.getHeight()) / 2 - child.getTop();
        final int leftOffset = (parent.getWidth() - child.getWidth()) / 2 - child.getLeft();

        if (topOffset != 0) {
            ViewCompat.offsetTopAndBottom(child, topOffset);
        }
        if (leftOffset != 0) {
            ViewCompat.offsetLeftAndRight(child, leftOffset);
        }
        return topOffset != 0 || leftOffset != 0;
    }
}