Detect when a ViewPager smoothScroll initialized by viewPager.setCurrentItem() has completed

gistfile1.txt

import android.support.v4.view.ViewPager;
import android.view.ViewTreeObserver;

/**
 * A class that can be added to a viewTreeObserver for ViewPager's in order to determine
 * when a smoothScroll transition is completed by viewPager.setCurrentItem();
 */
public class PagerScrollListener implements ViewTreeObserver.OnScrollChangedListener {
    private int scrollX;
    private int totalChange = 0;
    private OnTransitionCompleteListener onTransitionCompleteListener;
    private ViewPager viewPager;

    public PagerScrollListener(OnTransitionCompleteListener onTransitionCompleteListener, ViewPager viewPager) {
        this.scrollX = viewPager.getScrollX();
        this.onTransitionCompleteListener = onTransitionCompleteListener;
        this.viewPager = viewPager;
    }

    @Override
    public void onScrollChanged() {
        totalChange += Math.abs(scrollX - viewPager.getScrollX());
        scrollX = viewPager.getScrollX();
        if(totalChange == viewPager.getWidth()) {
            viewPager.getViewTreeObserver().removeOnScrollChangedListener(this);
            onTransitionCompleteListener.onTransitionComplete();
        }
    }

    public interface OnTransitionCompleteListener {
        void onTransitionComplete();
    }
}