Fragment疑問

//當Fragment中再次嵌套Fragment時，就用fm.getChildFragmentManager()來代替getFragmentManager()?
class GalleryAdapter extends FragmentPagerAdapter {
        int count = 3;// 默認10
        public GalleryAdapter(MainPage fm) {
            super(fm.getChildFragmentManager());
        }
        @Override
        public Fragment getItem(int position) {
            return fragments.get(position);
        }
        /**
         * 數量設置爲最大
         *
         * @return
         */
        @Override
        public int getCount() {
            return fragments.size();
        }
        /**
         * 真實數量
         *
         * @return
         */
        public int getRealCount() {
            return this.count;
        }
    }