带有由 LoaderManager 管理的自定义适配器的 AlphabetIndexer

Posted 2023-04-14

【中文标题】带有由 LoaderManager 管理的自定义适配器的 AlphabetIndexer

【英文标题】：AlphabetIndexer with Custom Adapter managed by LoaderManager

【发布时间】：2012-04-30 17:46:36

【问题描述】：

我正在尝试使用这样的自定义适配器实现AlphabetIndexer

AlphabetIndexer with Custom Adapter

我的类 ContactsCursorAdapter 扩展 SimpleCursorAdapter 并实现 SectionIndexer 我正在使用LoaderManager 来管理我的适配器的光标，所以我已经覆盖了swapCursor() 方法，就像上面示例的第二个答案所示。

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);
    

但是，如果我将列表视图设置为 fastScrollEnabled = true，则会出现此错误

getListView().setFastScrollEnabled(true);

在我的类 ContactsCursorLoaderListFragment 中扩展 ListFragment 并实现 LoaderManager.LoaderCallbacks 。

这是堆栈跟踪：

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 ComponentInfocom.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

在调用setFastScrollEnabled() 方法后，它会调用自定义适配器的getSections() 方法，这就是它崩溃的地方。

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);
           

    

如果我评论 setFastScrollEnabled() 调用，那么它不会出错，但我看不到 AlphabetIndexer 工作。

由于我的自定义适配器设置在ListFragment 而不是ListActivity，因此是否需要以不同方式实现？

有人对如何使这一切正常工作有任何建议吗？

【参考方案1】：

所以我终于让它工作了。我是这样做的：

我补充说：

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

像这样换入新光标后的onLoadFinished()方法

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，这三个语句从我的自定义 ListFragment 的 onActivityCreated() 方法中删除。

【讨论】：

如果没有数据而不是抛出空指针异常，让你的getSections 方法返回一个空列表不是更好吗？

是的，如果数据不可用，最好返回一个空列表，但是 getSections() 应该在光标被交换后调用，因为这是实现 CursorLoader。跨度>

只是在此处添加我的两分钱：这仅在您从未设置 setListShown(false); 时才有效加载出现。否则，除非您用新数据（与实际数据不同）刷新光标，否则快速滚动将永远不会出现