title: Incompatible types: Fragment cannot be converted to NavigationDrawerFragment
body: <p>I've been working on an app using API 14, but I had to downgrade to API 10. the app has fragments and activity fragments, I have imported the libraries and used the <code>getFragmentSupportManager</code> because it is v4. However, I have following error:</p>
  
  <p><img src="https://i.stack.imgur.com/ZyMlc.png" alt="enter image description here"></p>
  
  <p>I created a dummy app with Drawer layout and fragments with API 10 from the beginning, it had the same line in <code>MyActivity</code> file and it was not an error. Here is my code: </p>
  
  <pre><code>package az.test2;
  
  import android.app.Activity;
  import android.os.Bundle;
  import android.view.LayoutInflater;
  import android.view.Menu;
  import android.view.MenuItem;
  import android.view.View;
  import android.view.ViewGroup;
  import android.support.v4.widget.DrawerLayout;
  import android.support.v7.app.ActionBarActivity;
  import android.support.v7.app.ActionBar;
  import android.support.v4.app.Fragment;
  import android.support.v4.app.FragmentManager;
  import android.view.Gravity;
  
  
  public class MyActivity extends ActionBarActivity
      implements NavigationDrawerFragment.NavigationDrawerCallbacks {
  
      /**
       * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
       */
      private NavigationDrawerFragment mNavigationDrawerFragment;
  
      /**
       * Used to store the last screen title. For use in {@link #restoreActionBar()}.
       */
      private CharSequence mTitle;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_my);
  
          mNavigationDrawerFragment = (NavigationDrawerFragment)
             getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
          mTitle = getTitle();
  
          // Set up the drawer.
          mNavigationDrawerFragment.setUp(
              R.id.navigation_drawer,
              (DrawerLayout) findViewById(R.id.drawer_layout));
  
      }
  
      @Override
      public void onNavigationDrawerItemSelected(int position) {
          // update the main content by replacing fragments
          android.support.v4.app.FragmentManager lolo;
  
          FragmentManager FM = getSupportFragmentManager();
          FragAV fav = new FragAV();
          FragW fw = new FragW();
  
          switch (position){
              case 0:
                  FM.beginTransaction()
                      .replace(R.id.container, fav).commit();
                  break;
              case 1:
                  FM.beginTransaction()
                      .replace(R.id.container, fw).commit();
                  break;
              case 2: break;
          }
  
  
          //FM.beginTransaction().replace(R.id.container, PlaceholderFragment.newInstance(position + 1)).commit();
  
      }
  
      public void onSectionAttached(int number) {
          switch (number) {
              case 1:
                  mTitle = getString(R.string.title_section1);
                  break;
              case 2:
                  mTitle = getString(R.string.title_section2);
                  break;
              case 3:
                  mTitle = getString(R.string.title_section3);
                  break;
          }
      }
  
      public void restoreActionBar() {
          ActionBar actionBar = getSupportActionBar();
          actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
          actionBar.setDisplayShowTitleEnabled(true);
          actionBar.setTitle(mTitle);
      }
  
      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
          if (!mNavigationDrawerFragment.isDrawerOpen()) {
              // Only show items in the action bar relevant to this screen
              // if the drawer is not showing. Otherwise, let the drawer
              // decide what to show in the action bar.
              getMenuInflater().inflate(R.menu.my, menu);
              restoreActionBar();
  
              return true;
          }
          return super.onCreateOptionsMenu(menu);
      }
  
      @Override
      public boolean onOptionsItemSelected(MenuItem item) {
          // Handle action bar item clicks here. The action bar will
          // automatically handle clicks on the Home/Up button, so long
          // as you specify a parent activity in AndroidManifest.xml.
          int id = item.getItemId();
          if (id == R.id.action_settings) {
              return true;
          }
          return super.onOptionsItemSelected(item);
      }
  
      /**
       * A placeholder fragment containing a simple view.
       */
      public static class PlaceholderFragment extends Fragment {
          /**
           * The fragment argument representing the section number for this
           * fragment.
           */
          private static final String ARG_SECTION_NUMBER = "section_number";
  
          /**
           * Returns a new instance of this fragment for the given section
           * number.
           */
          public static PlaceholderFragment newInstance(int sectionNumber) {
              PlaceholderFragment fragment = new PlaceholderFragment();
              Bundle args = new Bundle();
              args.putInt(ARG_SECTION_NUMBER, sectionNumber);
              fragment.setArguments(args);
              return fragment;
          }
  
          public PlaceholderFragment() {
          }
  
          @Override
          public View onCreateView(LayoutInflater inflater, ViewGroup container,
              Bundle savedInstanceState) {
              View rootView = inflater.inflate(R.layout.fragment_my, container, false);
              return rootView;
          }
  
          @Override
          public void onAttach(Activity activity) {
              super.onAttach(activity);
              ((MyActivity) activity).onSectionAttached(
                  getArguments().getInt(ARG_SECTION_NUMBER));
          }
      }
  }
  </code></pre>
  
  <p>I did everything I could but this error seems to be very rare. any help would be much appreciated.</p>