title: isValidFragment Android API 19
body: <p>When I try my app with Android KitKat I have an error in PreferenceActivity.</p>
  <blockquote>
  <p>Subclasses of PreferenceActivity must override isValidFragment(String) to verify that the Fragment class is valid! com.crbin1.labeltodo.ActivityPreference has not checked if fragment com.crbin1.labeltodo.StockPreferenceFragment is valid</p>
  </blockquote>
  <p>In documentation I find the following explanation</p>
  <blockquote>
  <p>protected boolean isValidFragment (String fragmentName)</p>
  <p>Added in API level 19</p>
  <p>Subclasses should override this method and verify that the given fragment is a valid type to be attached to this activity. The default implementation returns true for apps built for android:targetSdkVersion older than KITKAT. For later versions, it will throw an exception.</p>
  </blockquote>
  <p>I don't find any example to resolve the problem.</p>