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POSimpleCursorTreeAdapter and CursorLoader for ExpandableListView
 

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    <p>I am trying to asynchronously query a provider by using a <code>CursorLoader</code> with a <code>SimpleCursorTreeAdapter</code> </p> <p>Here is my <code>Fragment</code> class which implements the <code>CursorLoader</code> </p> <pre><code>public class GroupsListFragment extends ExpandableListFragment implements LoaderManager.LoaderCallbacks&lt;Cursor&gt; { private final String DEBUG_TAG = getClass().getSimpleName().toString(); 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&lt;Cursor&gt; onCreateLoader(int id, Bundle args) { // This is called when a new Loader needs to be created. Log.d(DEBUG_TAG, "onCreateLoader for loader_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&lt;Cursor&gt; loader, Cursor data) { // Swap the new cursor in. int id = loader.getId(); Log.d(DEBUG_TAG, "onLoadFinished() for loader_id " + id); if (id != -1) { // child cursor if (!data.isClosed()) { Log.d(DEBUG_TAG, "data.getCount() " + data.getCount()); 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&lt;Cursor&gt; loader) { // This is called when the last Cursor provided to onLoadFinished() // is about to be closed. int id = loader.getId(); Log.d(DEBUG_TAG, "onLoaderReset() for loader_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); } } </code></pre> <p>And here is my adapter which subclasses <code>SimpleCursorTreeAdapter</code> </p> <pre><code>public class GroupsAdapter extends SimpleCursorTreeAdapter { private final String DEBUG_TAG = getClass().getSimpleName().toString(); 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 groupId = groupCursor.getInt(groupCursor .getColumnIndex(ContactsContract.Groups._ID)); Log.d(DEBUG_TAG, "getChildrenCursor() for groupId " + groupId); Loader loader = mActivity.getLoaderManager().getLoader(groupId); if ( loader != null &amp;&amp; loader.isReset() ) { mActivity.getLoaderManager().restartLoader(groupId, null, mFragment); } else { mActivity.getLoaderManager().initLoader(groupId, null, mFragment); } } } </code></pre> <p>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. </p> <p>1) Either the group opens up and the children appear below it</p> <p>2) The group does not open and the <code>setChildrenCursor()</code> call throws an <code>NullPointerException</code> error which gets caught in the try catch block</p> <p>3) The group does not open and no error is thrown</p> <p>Here is some debugging output in a scenario in which a group is expanded and showing the children:</p> <p>When all groups are displayed it ouputs:</p> <pre><code>05-20 10:08:22.765: D/GroupsListFragment(22132): onCreateLoader for loader_id -1 05-20 10:08:23.613: D/GroupsListFragment(22132): onLoadFinished() for loader_id -1 </code></pre> <p>-1 is the loader_id of the group cursor</p> <p>Then if i select one group in particular (let's just call it group A) it outputs:</p> <pre><code>05-20 23:22:31.140: D/GroupsAdapter(13844): getChildrenCursor() for groupId 67 05-20 23:22:31.140: D/GroupsListFragment(13844): onCreateLoader for loader_id 67 05-20 23:22:31.254: D/GroupsListFragment(13844): onLoadFinished() for loader_id 67 05-20 23:22:31.254: D/GroupsListFragment(13844): data.getCount() 4 05-20 23:22:31.254: W/GroupsListFragment(13844): Adapter expired, try again on the next query: null </code></pre> <p>The group does not expand and the <code>NullPointerException</code> is caught. Then if i select another group (let's just call it group B) it outputs:</p> <pre><code>05-20 23:25:38.089: D/GroupsAdapter(13844): getChildrenCursor() for groupId 3 05-20 23:25:38.089: D/GroupsListFragment(13844): onCreateLoader for loader_id 3 05-20 23:25:38.207: D/GroupsListFragment(13844): onLoadFinished() for loader_id 3 05-20 23:25:38.207: D/GroupsListFragment(13844): data.getCount() 6 </code></pre> <p>This time, the <code>NullPointerException</code> is not thrown. And instead of group B expanding, group A is expanded.</p> <p>Can anyone explain the behavior that the <code>setChildrenCursor()</code> call is exhibiting?</p> <p>I am thinking there is a problem with how the group/child CursorLoaders are instantiated in <code>onCreateLoader()</code>. For the group <code>CursorLoader</code> i just want all groups in my phone. The child <code>CursorLoader</code> should contain all contacts within a group. Does anyone have any ideas what could be the issue?</p> <p><strong>UPDATE</strong></p> <p>Thanks to @Yam's advice I have now modified the <code>getChildrenCursor()</code> method. I am now selecting the groupCursor position not the value of ContactsContract.Groups._ID to pass into the initLoader() call. I also changed the logic to call restartLoader() only when loader is not null and loader isReset is false.</p> <pre><code>protected Cursor getChildrenCursor(Cursor groupCursor) { // Given the group, we return a cursor for all the children within that // group int groupPos = groupCursor.getPosition(); Log.d(DEBUG_TAG, "getChildrenCursor() for groupPos " + groupPos); Loader loader = mActivity.getLoaderManager().getLoader(groupPos); if (loader != null &amp;&amp; !loader.isReset()) { mActivity.getLoaderManager().restartLoader(groupPos, null, mFragment); } else { mActivity.getLoaderManager().initLoader(groupPos, null, mFragment); } return null; } </code></pre> <p>This definitely makes more sense and does not exhibit some of the erratic behavior of a group expanding sometimes and not other times. </p> <p>However, there are contacts that are being displayed under a group that they don't belong to. And also some groups that do have contacts in them but it won't show any contacts. So it seems that the <code>getChildrenCursor()</code> issues may now be resolved. </p> <p>But now it looks to be an issue of how the CursorLoaders are instantiated in the <code>onCreateLoader()</code> method. Is the <code>CursorLoader</code> returned in the <code>onCreateLoader()</code> method for the child cursor being instantiated improperly? </p> <p><strong>UPDATE</strong></p> <p>So I have identified one of my issues. In the <code>getChildrenCursor()</code> method if I pass the groupId into the <code>initLoader()</code> method then in the <code>onCreateLoader()</code> method, when the <code>CursorLoader</code> is created it will get the correct groupid parameter for the query. However, in the <code>onLoadFinished()</code> the call to <code>setChildrenCursor()</code> is getting passed the loader id for the first parameter not the groupPosition. I'm guessing i have to map loader ids to group positions in some data structure. But i'm not sure if this is the best approach. Does anyone have any suggestions?</p>
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    1. COI've just done this, but it wasn't using a CursorLoader, so that's throwing me... In my implemmentation, the getChildrenCursor returns a cursor. With the loadermanager, where is that cursor/data actually going? If you are not feeding a cursor into the constructor, what is being fed into `getChildrenCursor` as the groupCursor?
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    2. COThe groupCursor has been set in the onLoadFinished() method of the LoaderManager. I have stepped through the code with a debugger and in the getChildenCursor() method, the groupCursor is always defined.
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    3. COI dunno, it really sounds like you aren't always getting a populated childCursor...
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