title: How do handle onBackPressed() in Fragment?
body: <p>This is my class name</p>
  
  <pre><code>public class PrimaryFragment extends Fragment implements OnRestartRequest {
  
      @Override
      public void onBackPressed() {
          if (mCardStackLayout.isCardSelected()) {
              mCardStackLayout.restoreCards();
          } else {
              super.onBackPressed();
          }
      }
  </code></pre>
  
  <p>Error on this line: <code>super.onBackPressed();</code></p>
  
  <p>I don't know what's the problem in fragment class's on back pressed button.</p>