Android:片段中的ActionBar

Question

我正在向GridFragment添加一个ActionBar，如下所示：

public class ImageGridFragment extends AbsListViewBaseFragment implements ActionBar.OnNavigationListener 
{       
    //ActionBar
    private ActionBar actionBar;
    private ArrayList<SpinnerNavItem> navSpinner;   // Title navigation Spinner data
    private TitleNavigationAdapter adapter; // Navigation adapter
    private MenuItem refreshMenuItem; // Refresh menu item

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

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) 
    {
        View rootView = inflater.inflate(R.layout.fr_image_grid, container, false);
        listView = (GridView) rootView.findViewById(R.id.grid);
        ((GridView) listView).setAdapter(new ImageAdapter());
        listView.setOnItemClickListener(new OnItemClickListener() 
        {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) 
            {
                TextView xx = (TextView) view.findViewById(R.id.grid_photo_id);
                String xxx = xx.getText().toString();
                Constants.gridview_photo_id_clicked = Integer.parseInt(xxx);
                startImageListViewActivity(position);
            }
        });

        actionBar = getActivity().getActionBar();
        actionBar.setDisplayShowTitleEnabled(false);    // LINE 100, NPE
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);    // Enabling Spinner dropdown navigation

        // Spinner title navigation data
        navSpinner = new ArrayList<SpinnerNavItem>();
        navSpinner.add(new SpinnerNavItem("Local", R.drawable.ic_location));
        navSpinner.add(new SpinnerNavItem("My Places", R.drawable.ic_my_places));
        navSpinner.add(new SpinnerNavItem("Checkins", R.drawable.ic_checkin));
        navSpinner.add(new SpinnerNavItem("Latitude", R.drawable.ic_latitude));
        adapter = new TitleNavigationAdapter(getActivity(), navSpinner);    // title drop down adapter
        actionBar.setListNavigationCallbacks(adapter, this);    // assigning the spinner navigation
        // Changing the action bar icon
        // actionBar.setIcon(R.drawable.ico_actionbar);
        return rootView;
    }

Logcat：

10-01 01:27:01.716: E/AndroidRuntime(1588): Caused by: java.lang.NullPointerException
10-01 01:27:01.716: E/AndroidRuntime(1588):     at com.abc.abc3.fragment.ImageGridFragment.onCreateView(ImageGridFragment.java:100)
10-01 01:27:01.716: E/AndroidRuntime(1588):     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
10-01 01:27:01.716: E/AndroidRuntime(1588):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
10-01 01:27:01.716: E/AndroidRuntime(1588):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
10-01 01:27:01.716: E/AndroidRuntime(1588):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
10-01 01:27:01.716: E/AndroidRuntime(1588):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
10-01 01:27:01.716: E/AndroidRuntime(1588):     at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:570)
10-01 01:27:01.716: E/AndroidRuntime(1588):     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1188)
10-01 01:27:01.716: E/AndroidRuntime(1588):     at android.app.Activity.performStart(Activity.java:5382)
10-01 01:27:01.716: E/AndroidRuntime(1588):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2279)
10-01 01:27:01.716: E/AndroidRuntime(1588):     ... 11 more

问题：

如上所述，它在第100行出现NPE错误。我如何准确地在片段中添加ActionBar？应该在哪里宣布呢？

谢谢！！

Answer 1

以下是工作原理：

public class ImageGridFragment implements ActionBar.OnNavigationListener
{

// ActionBar
private ActionBar actionBar;
private ArrayList<SpinnerNavItem> navSpinner;   // Title navigation Spinner data
private TitleNavigationAdapter adapter;         // Navigation adapter

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

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) 
{
    View rootView = inflater.inflate(R.layout.fr_image_grid, container, false);
    listView = (GridView) rootView.findViewById(R.id.grid);
    ((GridView) listView).setAdapter(new ImageAdapter());
    listView.setOnItemClickListener(new OnItemClickListener() 
    {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) 
        {
            // actions 
        }
    });

    // ActionBar
    actionBar = getActivity().getActionBar();
    actionBar.setDisplayHomeAsUpEnabled(true);
    actionBar.setDisplayShowTitleEnabled(true);                             
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);            
    navSpinner = new ArrayList<SpinnerNavItem>();                           
    navSpinner.add(new SpinnerNavItem("All", R.drawable.icon_go));
    navSpinner.add(new SpinnerNavItem("Cat 1", R.drawable.icon_go));
    navSpinner.add(new SpinnerNavItem("Cat 2", R.drawable.icon_go));
    adapter = new TitleNavigationAdapter(getActivity().getApplicationContext(), navSpinner);
    actionBar.setListNavigationCallbacks(adapter, this);    
    return rootView;
}

@Override
public boolean onNavigationItemSelected(int itemPosition, long itemId) 
{
    // Action to be taken after selecting a spinner item
    return false;
}

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) 
{
    // Inflate the menu items for use in the action bar
    inflater.inflate(R.menu.action_grid_menu, menu);
    // Associate searchable configuration with the SearchView
    SearchManager searchManager = (SearchManager) getActivity().getSystemService(Context.SEARCH_SERVICE);
    SearchView searchView = (SearchView) menu.findItem(R.id.action_search).getActionView();
    searchView.setSearchableInfo(searchManager.getSearchableInfo(getActivity().getComponentName()));
}

@Override
public boolean onOptionsItemSelected(MenuItem item) 
{
    switch (item.getItemId()) 
    {
        case android.R.id.home:
            getActivity().finish();
            return true;                
        case R.id.action_search:
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}