AlphabetIndexer with Custom Adapter managed by LoaderManager

Question

I am trying to implement AlphabetIndexer with Custom Adapter like this

AlphabetIndexer with Custom Adapter

My class ContactsCursorAdapter extends SimpleCursorAdapter and implements SectionIndexer and I am using a LoaderManager to manage my adapter's cursor so i have overridden the swapCursor() method like the second answer to the example above indicates.

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);
    }
}

However, this errors out if I set my listview to fastScrollEnabled = true

getListView().setFastScrollEnabled(true);

in my class ContactsCursorLoaderListFragment which extends ListFragment and implements LoaderManager.LoaderCallbacks .

Here is the stack trace:

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

after the setFastScrollEnabled() method gets called it calls the custom adapter's getSections() method which is where it crashes.

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);
        }   

    }
}

And if I comment the setFastScrollEnabled() call, then it does not error out, but I do not see the AlphabetIndexer working.

Does this need to be implemented differently because my custom adapter is set in a ListFragment and not a ListActivity?

Does anyone have suggestions about how to make this all work?

Silvereye

Answer 1

So I finally got this to work. Here's how i did it:

I added:

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

to the onLoadFinished() method after the new cursor was swapped in like so

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);

}

consequently these three statements were removed from the onActivityCreated() method of my custom ListFragment.

Silvereye

Wouldn't it be better to just make your getSections method return an empty list if there's no data instead of throwing a null pointer exception? – Ampersand

Yes it would be a good idea to return an empty list if the data is not available, however the getSections() should be called after the cursor is swapped in since this is implementing a CursorLoader. – Silvereye

just adding my two cents here: this only works if you never set the setListShown(false); for the loading to appear. Otherwise the fastscroll will never appear until you refresh the cursor with new data (diferent than the actual) – Elastomer