ExpandableListView using SimpleCursorTreeAdapter scrolls to top on update

Question

I have created an ExpandableListAdapter by extending SimpleCursorTreeAdapter. The cursors are managed by loaders. When the list is displayed to user , I start a background service to fetch latest data from server. If the server returns new data I add it to DB and notify the children cursors. The cursors gets requeried and the list updates. At this point if the user has scrolled down in the list, the list scrolls up to top. This is very annoying. I have gone through the entire API for *TreeAdapters and do not see any method to prevent it. This must be a very common problem. How can I fix it ?

Answer 1

Try this code:

public class GroupsAdapter extends SimpleCursorTreeAdapter {

    private final String TAG = getClass().getSimpleName().toString();

    private final FragmentActivity mActivity;
    private final ContactsFragment mFragment;

    private static final String[] CONTACTS_PROJECTION = new String[] {
                    ContactsContract.Users._ID, ContactsContract.Users.USER_ID,
                    ContactsContract.Users.NAME, ContactsContract.Users.STATUS_TYPE,
                    ContactsContract.Users.STATUS_MESSAGE,
                    ContactsContract.Users.HAS_ALERT };

    // Note that the constructor does not take a Cursor. This is done to avoid
    // querying the database on the main thread.
    public GroupsAdapter(final Context context, final ContactsFragment glf,
                    final int groupLayout, final int childLayout,
                    final String[] groupFrom, final int[] groupTo,
                    final String[] childrenFrom, final int[] childrenTo) {

            super(context, null, groupLayout, groupFrom, groupTo, childLayout,
                            childrenFrom, childrenTo);
            mActivity = (FragmentActivity) context;
            mFragment = glf;
    }

    @Override
    protected Cursor getChildrenCursor(final Cursor groupCursor) {
            final String id = groupCursor.getString(groupCursor
                            .getColumnIndex(ContactsContract.Groups.GROUP_ID));
            final CursorLoader cursorLoader = new CursorLoader(mActivity,
                            ContactsContract.Users.CONTENT_URI, CONTACTS_PROJECTION, "("
                                            + ContactsContract.UserGroupColumns.GROUP_ID + "=?)",
                            new String[] { id }, null);

            Cursor childCursor = null;

            try {
                    childCursor = cursorLoader.loadInBackground();
                    childCursor.moveToFirst();
            } catch (final Exception e) {
                    Log.e(TAG, e.getMessage());
            }

            return childCursor;

    }

}

and the fragment:

public class ContactsFragment extends Fragment implements
            LoaderCallbacks<Cursor> {

    private static final String[] GROUPS_PROJECTION = new String[] {
                    ContactsContract.Groups._ID, ContactsContract.Groups.NAME,
                    ContactsContract.Groups.GROUP_ID,
                    ContactsContract.Groups.USERS_COUNT };
    private static final String TAG = "ContactsFragment";

    ExpandableListView listView;
    GroupsAdapter mAdapter;

    public ContactsFragment() {
            // Required empty public constructor
    }

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

    @Override
    public View onCreateView(final LayoutInflater inflater,
                    final ViewGroup container, final Bundle savedInstanceState) {
            // Inflate the layout for this fragment
            return inflater.inflate(R.layout.fragment_contacts, container, false);
    }

    @Override
    public void onCreateOptionsMenu(final Menu menu, final MenuInflater inflater) {
            inflater.inflate(R.menu.contacts_menu, menu);
            super.onCreateOptionsMenu(menu, inflater);
    }

    @Override
    public void onActivityCreated(final Bundle savedInstanceState) {

            super.onActivityCreated(savedInstanceState);

            listView = (ExpandableListView) getView().findViewById(
                            android.R.id.list);
            // listView.setEmptyView();
            // Set up our adapter
            mAdapter = new GroupsAdapter(getActivity(), R.layout.group,
                            R.layout.user, new String[] { ContactsContract.Groups.NAME,
                                            ContactsContract.Groups.USERS_COUNT }, // Name
                            // for group layouts
                            new int[] { R.id.group, R.id.count }, new String[] {
                                            ContactsContract.Users.NAME,
                                            ContactsContract.Users.STATUS_MESSAGE }, // Name
                            // for child layouts
                            new int[] { R.id.user_name, R.id.status_message });

            listView.setAdapter(mAdapter);

            // Prepare the loader. Either re-connect with an existing one,
            // or start a new one.
            final Loader<Cursor> loader = getLoaderManager().getLoader(-1);
            if (loader != null && !loader.isReset()) {
                    getLoaderManager().restartLoader(-1, null, this);
            } else {
                    getLoaderManager().initLoader(-1, null, this);
            }
            getActivity().getContentResolver().registerContentObserver(
                            ContactsContract.Users.CONTENT_URI, false,
                            new ContentObserver(null) {
                                    @Override
                                    public void onChange(final boolean selfChange) {
                                            Log.w(TAG, "Change");
                                    }
                            });
    }

    @Override
    public Loader<Cursor> onCreateLoader(final int id, final Bundle args) {
            // This is called when a new Loader needs to be created.
            // group cursor
            final CursorLoader cl = new CursorLoader(getActivity(),
                            ContactsContract.Groups.CONTENT_URI, GROUPS_PROJECTION, null,
                            null, null);

            return cl;
    }

    @Override
    public void onLoadFinished(final Loader<Cursor> loader, final Cursor cursor) {

            // Swap the new cursor in.
            final int id = loader.getId();

            if (id == -1) {

                    mAdapter.setGroupCursor(cursor);

            }

    }

    @Override
    public void onLoaderReset(final Loader<Cursor> loader) {
            // This is called when the last Cursor provided to onLoadFinished()
            // is about to be closed.
            final int id = loader.getId();
            if (id != -1) {
                    // child cursor
                    try {
                            mAdapter.setChildrenCursor(id, null);
                    } catch (final NullPointerException e) {
                            Log.w("TAG", "Adapter expired, try again on the next query: "
                                            + e.getMessage());
                    }
            } else {
                    mAdapter.setGroupCursor(null);
            }
    }

}