title: getActivity() returns null on fragment?
body: <p>I have <code>MainActivity()</code> and a <code>FirstFragment()</code>. </p>
  
  <p>I'm calling a function which is in FirstFragment from <code>MainActivity()</code>. </p>
  
  <p>The problem is, that time <code>getActivity()</code> returns null ? </p>