AlphabetIndexer與自定義適配器通過LoaderManager

Question

管理我想實現AlphabetIndexer與自定義適配器這樣

AlphabetIndexer with Custom Adapter

我班ContactsCursorAdapter擴展SimpleCursorAdapter並實現SectionIndexer 和我使用的是LoaderManager來管理我的適配器的光標所以我已經覆蓋了swapCursor()方法，就像上面示例的第二個答案所示。

public class ContactsCursorAdapter extends SimpleCursorAdapter 
    implements SectionIndexer{ 

    private LayoutInflater mInflater; 
    private Context mContext; 

    private AlphabetIndexer mAlphaIndexer; 

    public ContactsCursorAdapter(Context context, int layout, Cursor c, 
     String[] from, int[] to) { 
     super(context, layout, c, from, to); 

     mInflater = LayoutInflater.from(context); 
     mContext = context; 
    } 

    public View getView(final int position, View convertView, ViewGroup parent) { 
     ... 
    } 

    @Override 
    public int getPositionForSection(int section) { 
     return mAlphaIndexer.getPositionForSection(section); 
    } 

    @Override 
    public int getSectionForPosition(int position) { 
     return mAlphaIndexer.getSectionForPosition(position); 
    } 

    @Override 
    public Object[] getSections() { 
     return mAlphaIndexer.getSections(); 
    } 

    public Cursor swapCursor(Cursor c) { 
     // Create our indexer 
     if (c != null) { 
      mAlphaIndexer = new AlphabetIndexer(c, c.getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME), 
       " ABCDEFGHIJKLMNOPQRSTUVWXYZ"); 
     } 
     return super.swapCursor(c); 
    } 
} 

然而，這樣的錯誤，如果我把我的列表視圖來fastScrollEnabled =真

getListView（）setFastScrollEnabled（真）。

在我的課ContactsCursorLoaderListFragment其中擴展ListFragment並實現LoaderManager.LoaderCallbacks。

這裏是堆棧跟蹤：

04-25 01:37:23.280: E/AndroidRuntime(711): FATAL EXCEPTION: main 
04-25 01:37:23.280: E/AndroidRuntime(711): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sendit/com.sendit.ContactManager}: java.lang.NullPointerException 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.access$600(ActivityThread.java:123) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.os.Handler.dispatchMessage(Handler.java:99) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.os.Looper.loop(Looper.java:137) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.main(ActivityThread.java:4424) 
04-25 01:37:23.280: E/AndroidRuntime(711): at java.lang.reflect.Method.invokeNative(Native Method) 
04-25 01:37:23.280: E/AndroidRuntime(711): at java.lang.reflect.Method.invoke(Method.java:511) 
04-25 01:37:23.280: E/AndroidRuntime(711): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
04-25 01:37:23.280: E/AndroidRuntime(711): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
04-25 01:37:23.280: E/AndroidRuntime(711): at dalvik.system.NativeStart.main(Native Method) 
04-25 01:37:23.280: E/AndroidRuntime(711): Caused by: java.lang.NullPointerException 
04-25 01:37:23.280: E/AndroidRuntime(711): at com.sendit.ContactsCursorAdapter.getSections(ContactsCursorAdapter.java:222) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.widget.FastScroller.getSectionsFromIndexer(FastScroller.java:507) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.widget.FastScroller.init(FastScroller.java:269) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.widget.FastScroller.<init>(FastScroller.java:155) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.widget.AbsListView.setFastScrollEnabled(AbsListView.java:1144) 
04-25 01:37:23.280: E/AndroidRuntime(711): at com.sendit.LoaderCursor$ContactsCursorLoaderListFragment.onActivityCreated(LoaderCursor.java:107) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:847) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1032) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.BackStackRecord.run(BackStackRecord.java:622) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1382) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.Activity.performStart(Activity.java:4474) 
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1929) 
04-25 01:37:23.280: E/AndroidRuntime(711): ... 11 more 

後setFastScrollEnabled()方法被調用，它調用自定義適配器的getSections()方法，這是它崩潰。

public class LoaderCursor extends Activity { 

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

     FragmentManager fm = getFragmentManager(); 

     // Create the list fragment and add it as our sole content. 
     if (fm.findFragmentById(android.R.id.content) == null) { 
      ContactsCursorLoaderListFragment list = new ContactsCursorLoaderListFragment(); 
      fm.beginTransaction().add(android.R.id.content, list).commit(); 
     } 
    } 

    public static class ContactsCursorLoaderListFragment extends ListFragment 
     implements LoaderManager.LoaderCallbacks<Cursor> { 

     ContactsCursorAdapter mAdapter; 
     Cursor mCursor; 
     String mCurFilter; 

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

      populateContactList(); 

      // Prepare the loader. Either re-connect with an existing one, 
      // or start a new one. 
      getLoaderManager().initLoader(0, null, this); 

      ListView lv = getListView(); 
      lv.setFastScrollEnabled(true); 
      //lv.setScrollingCacheEnabled(true); 
      lv.setDivider(getResources().getDrawable(R.drawable.list_divider)); 

     }  

     // These are the Contacts rows that we will retrieve. 
     final String[] CONTACTS_SUMMARY_PROJECTION = new String[] { 
      ContactsContract.Contacts._ID, 
      ContactsContract.Contacts.DISPLAY_NAME, 
      ContactsContract.Contacts.PHOTO_ID, }; 

     public Loader<Cursor> onCreateLoader(int id, Bundle args) { 
      // This is called when a new Loader needs to be created. This 
      // sample only has one Loader, so we don't care about the ID. 
      // First, pick the base URI to use depending on whether we are 
      // currently filtering. 
      Uri baseUri; 
      if (mCurFilter != null) { 
       baseUri = Uri.withAppendedPath(ContactsContract.Contacts.CONTENT_FILTER_URI,Uri.encode(mCurFilter)); 
      } else { 
       baseUri = ContactsContract.Contacts.CONTENT_URI; 
      } 

      // Now create and return a CursorLoader that will take care of 
      // creating a Cursor for the data being displayed. 
      String selection = "((" + ContactsContract.Contacts.DISPLAY_NAME + 
       " NOTNULL) AND (" + ContactsContract.Contacts.HAS_PHONE_NUMBER + "=1) 
       AND (" + ContactsContract.Contacts.DISPLAY_NAME + " != ''))"; 
      String sortOrder = ContactsContract.Contacts.DISPLAY_NAME 
       + " COLLATE LOCALIZED ASC"; 

      return new CursorLoader(getActivity(), baseUri, 
       CONTACTS_SUMMARY_PROJECTION, selection, null, sortOrder); 

     } 

     public void onLoadFinished(Loader<Cursor> loader, Cursor data) { 
      // Swap the new cursor in. (The framework will take care of closing the 
      // old cursor once we return.) 
      mAdapter.swapCursor(data); 
     } 

     public void onLoaderReset(Loader<Cursor> loader) { 
      // This is called when the last Cursor provided to onLoadFinished() 
      // above is about to be closed. We need to make sure we are no 
      // longer using it. 
      mAdapter.swapCursor(null); 
     } 

     /** 
     * Populate the contact list 
     */ 
     private void populateContactList() { 

      // start mappings 
      String[] from = new String[] { ContactsContract.Contacts.DISPLAY_NAME }; 
      int[] to = new int[] { R.id.contactInfo }; 

      // Create an empty adapter we will use to display the loaded data. 
      mAdapter = new ContactsCursorAdapter(getActivity().getApplicationContext(),  
       R.layout.contact_manager, null, from, to); 
      setListAdapter(mAdapter); 
     } 

    } 
} 

如果我評論了setFastScrollEnabled()通話，那麼它不報錯了，但我沒有看到AlphabetIndexer工作。

這是否需要以不同的方式實現，因爲我的自定義適配器設置爲ListFragment而不是ListActivity？

有沒有人有關於如何使這一切工作的建議？

Answer 1

所以我終於得到了這個工作。以下是我做的：

我說：

ListView lv = getListView(); 
lv.setFastScrollEnabled(true); 
lv.setScrollingCacheEnabled(true); 

到onLoadFinished()方法新的光標被換在像這樣

public void onLoadFinished(Loader<Cursor> loader, Cursor data) { 
// Swap the new cursor in. (The framework will take care of closing the 
// old cursor once we return.) 
mAdapter.swapCursor(data); 

ListView lv = getListView(); 
lv.setFastScrollEnabled(true); 
lv.setScrollingCacheEnabled(true); 

} 

因此這三個語句是從onActivityCreated()方法去除後我的自定義ListFragment。