title: What is the role of " isViewFromObject (View view, Object object)" in FragmentStatePagerAdapter?
body: <p>I am using a <code>FragmentStatePagerAdapter</code> with my View Pager. The Fragment returned is not displayed on the screen if <code>isViewFromObject (View view, Object object)</code> returns <code>false</code>. Why is that? <br>
  The developer doc says <code>Determines whether a page View is associated with a specific key object as returned by instantiateItem(ViewGroup, int). This method is required for a PagerAdapter to function properly.</code> But I am not clear with this definition. </p>