在导航抽屉项上切换片段单击

Question

我在我的应用程序中使用抽屉菜单，并实现了在NavigationDrawer片段类中切换片段的逻辑。我最近读到片段切换只能从托管活动中发生。

有一个从NavigationDrawerFragment调用的接口，用于通知导航抽屉列表视图中所选位置的MainActivity。

public static interface NavigationDrawerCallbacks {
    /**
     * Called when an item in the navigation drawer is selected.
     */
    void onNavigationDrawerItemSelected(int position);
} 

我感到困惑的是，在Mainactive中有一个静态片段，它是使用NavigationDrawer片段中接口提供的位置调用的。

@Override
public void onNavigationDrawerItemSelected(int position) {

    FragmentManager fragmentManager = getFragmentManager(); 
    fragmentManager
            .beginTransaction()
            .replace(R.id.container,
                    PlaceholderFragment.newInstance(position)).commit();

}

PlaceHolderFragment类如下所示：

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 Fragment 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_main, container,
                false);
        return rootView;
    }

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

目前我的碎片交易是这样发生的：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    mDrawerListView = (ListView) inflater.inflate(
            R.layout.fragment_navigation_drawer, container, false);
    mDrawerListView
            .setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view,
                        int position, long id) {
                    selectItem(position);
                    Fragment fragment;
                    FragmentManager fManager = getFragmentManager();

                    int count = fManager.getBackStackEntryCount();
                    for (int i = 0; i < count; ++i) {

                        fManager.popBackStackImmediate();
                        Log.e("NavFrag", "Popped frag" + i);
                    }
                    FragmentTransaction fTransaction = fManager
                            .beginTransaction();
                    switch (position) {
                    case 0:
                        fragment = new MCTrackFragment();
                        fTransaction.replace(R.id.container, fragment)

                                .commit();
                        break;
                    case 1:
                        fragment = new MCPlaylistFragment();
                        fTransaction.replace(R.id.container, fragment)
                                .commit();
                        break;
                    case 2:
                        fragment = new MCOfflineSongs();
                        fTransaction.replace(R.id.container, fragment)
                                .commit();
                        break;
                    case 3:
                        fragment = new MCOwnFeed();
                        fTransaction.replace(R.id.container, fragment)
                                .commit();
                        break;
                    case 4:
                        fragment = new MCCategories();
                        fTransaction.replace(R.id.container, fragment)
                                .commit();
                        break;
                    }
                }
            });
    mDrawerListView.setAdapter(new ArrayAdapter<String>(getActionBar()
            .getThemedContext(),
            android.R.layout.simple_list_item_activated_1,
            android.R.id.text1, new String[] {
                    getString(R.string.title_section1),
                    getString(R.string.title_section2),
                    getString(R.string.title_section3),
                    getString(R.string.title_section4),
                    getString(R.string.title_section5) }));
    mDrawerListView.setItemChecked(mCurrentSelectedPosition, true);
    return mDrawerListView;
}

当我们使用Navigationdrawer创建项目时，会自动生成占位符片段。

占位符片段用于什么？

我应该怎么做才能使片段事务在承载这些片段的活动内发生？

我尝试在接口实现中添加片段事务，但它不起作用。

感谢帮助，提前感谢

Answer 1

我们需要始终从活动中切换片段是正确的，因此我们需要从抽屉菜单片段向将要托管要显示的新片段的活动提供回调。在活动中，切换片段的代码如下：

@Override
public void onNavigationDrawerItemSelected(int position) {

    Fragment fragment;
    FragmentManager fManager = getFragmentManager();
    Bundle args = new Bundle();
    args.putInt(MCConstants.ARG_SECTION_NUMBER, position);
    clearAllBackStack();
    FragmentTransaction fTransaction = fManager.beginTransaction();
    if (MCMediaPlayerService.getInstance() != null) {
        MCMediaPlayerService.getInstance().stopMusic();

    }
    MCSelectedTrackIdSingleton.getInstance().mCurrentSongId = 0;
    MCSelectedSongIdSingleton.getInstance().mCurrentSongId = 0;

    switch (position) {
    case 0:
        fragment = new MCTrackFragment();
        fragment.setArguments(args);
        fTransaction.replace(R.id.container, fragment,
                MCConstants.TRACK_TAG).commit();
        break;
    case 1:
        fragment = new MCPlaylistFragment();
        fragment.setArguments(args);
        fTransaction.replace(R.id.container, fragment,
                MCConstants.PLAYLIST_TAG).commit();
        break;
    case 2:
        fragment = new MCOfflineSongs();
        fragment.setArguments(args);
        fTransaction.replace(R.id.container, fragment,
                MCConstants.OFFLINE_TAG).commit();
        break;
    case 3:
        fragment = new MCOwnFeed();
        fragment.setArguments(args);
        fTransaction.replace(R.id.container, fragment,
                MCConstants.OWNFEED_TAG).commit();
        break;
    case 4:
        fragment = new MCCategories();
        fragment.setArguments(args);
        fTransaction.replace(R.id.container, fragment,
                MCConstants.CATEGORIES_TAG).commit();
        break;
    }

}

抽屉菜单片段类的onCreate方法里面：

 @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Read in the flag indicating whether or not the user has demonstrated
    // awareness of the
    // drawer. See PREF_USER_LEARNED_DRAWER for details.
    SharedPreferences sp = PreferenceManager
            .getDefaultSharedPreferences(getActivity());
    mUserLearnedDrawer = sp.getBoolean(PREF_USER_LEARNED_DRAWER, false);

    if (savedInstanceState != null) {
        mCurrentSelectedPosition = savedInstanceState
                .getInt(STATE_SELECTED_POSITION);
        mFromSavedInstanceState = true;
    }

    // Select either the default item (0) or the last selected item.
    selectItem(mCurrentSelectedPosition); //Select item called
}

选择项目方法如下：

 private void selectItem(int position) {
    mCurrentSelectedPosition = position;
    if (mDrawerListView != null) {
        mDrawerListView.setItemChecked(position, true);
    }
    if (mDrawerLayout != null) {
        mDrawerLayout.closeDrawer(mFragmentContainerView);
    }
    if (mCallbacks != null) {
        mCallbacks.onNavigationDrawerItemSelected(position);
    }
}