片段类onCreate未调用

Question

最近我用eclipse创建了一个新的android项目（带导航抽屉），我用下面的代码在项目点击的布局之间切换

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
         View rootView=null;
            switch(getArguments().getInt(ARG_SECTION_NUMBER)) {
                case 1:
                    rootView = inflater.inflate(R.layout.layout_searchride, container, false);
                    break;
                case 2:
                    rootView = inflater.inflate(R.layout.layout_add_ride, container, false);
                    break;
                case 3:
                    rootView = inflater.inflate(R.layout.layout_ride_notification, container, false);
                    break;

            }
            return rootView;
    }

布局正在渲染并正常工作，但与之关联的类文件未被触发。所以没有调用任何类的onCreate函数。我知道它很愚蠢因为我没有打电话给班级。但问题出在哪里，我把这些类称为ti启动？

我的主要活动的完整代码是：

public class Dashboard extends Activity 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_dashboard);

    mNavigationDrawerFragment = (NavigationDrawerFragment) getFragmentManager()
            .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
    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager
            .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 = getActionBar();
    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.dashboard, 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=null;
            switch(getArguments().getInt(ARG_SECTION_NUMBER)) {
                case 1:
                    rootView = inflater.inflate(R.layout.layout_searchride, container, false);
                    break;
                case 2:
                    rootView = inflater.inflate(R.layout.layout_add_ride, container, false);
                    break;
                case 3:
                    rootView = inflater.inflate(R.layout.layout_ride_notification, container, false);
                    break;

            }
            return rootView;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((Dashboard) activity).onSectionAttached(getArguments().getInt(
                ARG_SECTION_NUMBER));
    }
}
}