@Override
    protected void onDestroy() {
        Log.d("TabbedViewPagerActivity.onDestroy");
        if (viewPager != null) {
            viewPager.unregisterOnPageChangeCallback(pageChangeCallback);
        }
        super.onDestroy();
    }
set if the pull-to-refresh gesture should be enabled for the displayed content
main/src/main/java/cgeo/geocaching/activity/TabbedViewPagerActivity.java