code: private void initializeFragments() {
          navigationFragment = (NavigationFragment) getSupportFragmentManager()
                  .findFragmentByTag(NAVIGATION_FRAGMENT_TAG);
  
          if (navigationFragment == null) {
              navigationFragment = (NavigationFragment) Fragment
                      .instantiate(this, NavigationFragment.class.getName());
              navigationFragment.setRetainInstance(true);
              navigationFragment.setCallback(this);
              FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
              transaction.add(R.id.navigation_fragment_container, navigationFragment,
                      NAVIGATION_FRAGMENT_TAG);
              transaction.commit();
          } else if (!navigationFragment.isAdapterCreated()) {
              navigationFragment.setCallback(this);
          }
  
          navigationFragment.setAdapterCallback(this);
          preferenceFragment = getSupportFragmentManager().findFragmentByTag(PREFERENCE_FRAGMENT_TAG);
          adaptNavigationSelectionColor();
          adaptNavigationDividerColor();
          adaptNavigationEnabledState();
      }
docs: Initializes the activity's fragments.