[android-developers] SimpleCursorTreeAdapter and CursorLoader

I am trying to asynchronously query a provider by using a CursorLoader with a SimpleCursorTreeAdapter

Here is my Fragment class which implements the CursorLoader

public class GroupsListFragment extends ExpandableListFragment implements
  LoaderManager.LoaderCallbacks<Cursor> {

  private static final String[] CONTACTS_PROJECTION = new String[] {
    ContactsContract.Contacts._ID,
    ContactsContract.Contacts.DISPLAY_NAME };

  private static final String[] GROUPS_SUMMARY_PROJECTION = new String[] {
    ContactsContract.Groups.TITLE, ContactsContract.Groups._ID,
    ContactsContract.Groups.SUMMARY_COUNT,
    ContactsContract.Groups.ACCOUNT_NAME,
    ContactsContract.Groups.ACCOUNT_TYPE,
    ContactsContract.Groups.DATA_SET };

  GroupsAdapter mAdapter;

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

    populateContactList();

    getLoaderManager().initLoader(-1, null, this);
  } 

  public Loader<Cursor> onCreateLoader(int id, Bundle args) {
    // This is called when a new Loader needs to be created.
    Log.d("DEBUG", "onCreateLoader for id " + id);
    CursorLoader cl;
    if (id != -1) {
      // child cursor
      Uri contactsUri = ContactsContract.Data.CONTENT_URI;
      String selection = "(("
        + ContactsContract.CommonDataKinds.GroupMembership.DISPLAY_NAME
        + " NOTNULL) AND ("
        + ContactsContract.CommonDataKinds.GroupMembership.HAS_PHONE_NUMBER
        + "=1) AND ("
        + ContactsContract.CommonDataKinds.GroupMembership.DISPLAY_NAME
        + " != '') AND ("
        + ContactsContract.CommonDataKinds.GroupMembership.GROUP_ROW_ID
        + " = ? ))";
      String sortOrder = ContactsContract.CommonDataKinds.GroupMembership.DISPLAY_NAME
        + " COLLATE LOCALIZED ASC";
      String[] selectionArgs = new String[] { String.valueOf(id) };

      cl = new CursorLoader(getActivity(), contactsUri,
        CONTACTS_PROJECTION, selection, selectionArgs, sortOrder);
    } else {
      // group cursor
      Uri groupsUri = ContactsContract.Groups.CONTENT_SUMMARY_URI;
      String selection = "((" + ContactsContract.Groups.TITLE
        + " NOTNULL) AND (" + ContactsContract.Groups.TITLE
        + " != '' ))";
      String sortOrder = ContactsContract.Groups.TITLE
        + " COLLATE LOCALIZED ASC";
      cl = new CursorLoader(getActivity(), groupsUri,
        GROUPS_SUMMARY_PROJECTION, selection, null, sortOrder);
    }

    return cl;
  }

  public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
    // Swap the new cursor in. 
    int id = loader.getId();
    Log.d("DEBUG", "onLoadFinished() for id " + id);
    if (id != -1) {
      // child cursor
      if (data != null && mAdapter != null) {
        if (!data.isClosed()) {
          try {
            mAdapter.setChildrenCursor(id, data);
          } catch (NullPointerException e) {
            Log.w("DEBUG","Adapter expired, try again on the next query: "
              + e.getMessage());
          }
        }
      }
    } else {
      mAdapter.setGroupCursor(data);
    }

  }

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

  /**
  * Populate the contact list
  */
  private void populateContactList() {
    // Set up our adapter
    mAdapter = new GroupsAdapter(getActivity(),this,
      android.R.layout.simple_expandable_list_item_1,
      android.R.layout.simple_expandable_list_item_1,
      new String[] { ContactsContract.Groups.TITLE }, // Name for group layouts
      new int[] { android.R.id.text1 },
      new String[] { ContactsContract.Contacts.DISPLAY_NAME }, // Name for child layouts
      new int[] { android.R.id.text1 });

    setListAdapter(mAdapter);
  }
}

And here is my adapter which subclasses SimpleCursorTreeAdapter

public class GroupsAdapter extends SimpleCursorTreeAdapter {

  private ContactManager mActivity;
  private GroupsListFragment mFragment;

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

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

  @Override
  protected Cursor getChildrenCursor(Cursor groupCursor) {
    // Given the group, we return a cursor for all the children within that group
    int id = groupCursor.getInt(groupCursor
      .getColumnIndex(ContactsContract.Groups._ID));

    mActivity.getLoaderManager().initLoader(id, null, mFragment);

    return null;
  }

}

The problem is that when i click one of the parent groups one of three things happens in what appears to be a inconsistent fashion.

1) Either the group opens up and the children appear below it

2) The group down not open and the setChildrenCursor() call throws an NullPointerException error which gets caught in the try catch block

3) The group does not open and no error is thrown

Can anyone explain the behavior that the setChildrenCursor() call is exhibiting?


http://stackoverflow.com/questions/10611927/simplecursortreeadapter-and-cursorloader

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