title: Whats is return by getChildAt of Fragment Pager Adapter?
body: <p>My FragmentPagerAdapter is some ListFragment.</p>
  
  <p>when scrolled Page,call  onPageSelected, I want run someMethod in ListFragment.</p>
  
  <p>but problem is  when I ill get Fragment,I tried this</p>
  
  <pre><code>public void onPageSelected(int position) {
                    ((MyListFragment)((Viewpager)viewPagerAdapter.getChildAt(position))).someMethod;
              }
  </code></pre>
  
  <p>but got error ,viewPager cant cast MyListFragment.</p>
  
  <p>how I get ListFragement?</p>