Android CursorLoader not responding to ContentProvider notifications

Question

I'm updating an Android 2.2 application to use CursorLoader (using the v4 compatibility library) and I'm tearing my hair out trying to understand why the onLoadFinished method is not called when the content provider notifies a change in the content associated with the CursorLoader query.

The CursorLoader is querying a customer content provider. My provider sets the notification URI in its query method:

cursor.setNotificationUri(getContext().getContentResolver(), uri);

and notifies changes in its insert/update/delete methods:

getContext().getContentResolver().notifyChange(uri, null);

I've checked that the URI is identical in both cases. Previously I was using a ManagedQuery with the same content provider and queried content was updated fine, which makes me think the content provider is probably ok.

I've looked at the LoaderCursorSupport example and, interestingly, when I run it on my Nexus One I don't see it reflect changes I make to contact names (switching between the example app and the contacts app). Should it? If so, is there some underlying problem I'm not aware of?

Answer 1

I finally got to the bottom of this and, as is usually the way, it was a stupid mistake on my part. I was calling cursor.close() in my onLoadFinished() method - I use the returned cursor to create an ArrayAdapter (I need to manually insert an item at the top of the list) and the cursor close was a leftover from using a ManagedQuery before migrating to use CursorLoader.

In the process of finding this, I created a simple test class to display a list of bookmarks and add a random bookmark (using the options menu). This worked as it should i.e. onLoadFinished() is called after the item is added. Here's the code in case it's useful for anyone else:

package com.test;

import android.content.ContentValues;
import android.database.Cursor;
import android.os.Bundle;
import android.provider.Browser;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.ListFragment;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.support.v4.view.MenuItemCompat;
import android.support.v4.widget.SimpleCursorAdapter;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;

public class CursorLoaderTestActivity extends FragmentActivity 
{
    private static final String TAG = CursorLoaderTestActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);

        FragmentManager fm = getSupportFragmentManager();

        // Create the list fragment and add it as our sole content.
        if (fm.findFragmentById(android.R.id.content) == null) 
        {
            CursorLoaderListFragment list = new CursorLoaderListFragment();
            fm.beginTransaction().add(android.R.id.content, list).commit();
        }
    }


    public static class CursorLoaderListFragment extends ListFragment implements LoaderManager.LoaderCallbacks<Cursor> 
    {

        // This is the Adapter being used to display the list's data.
        SimpleCursorAdapter mAdapter;

        // If non-null, this is the current filter the user has provided.
        String mCurFilter;

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

            // Give some text to display if there is no data.  In a real
            // application this would come from a resource.
            setEmptyText("No data");

            // We have a menu item to show in action bar.
            setHasOptionsMenu(true);

            // Create an empty adapter we will use to display the loaded data.
            mAdapter = new SimpleCursorAdapter(getActivity(),
                    android.R.layout.simple_list_item_1, null,
                    new String[] { Browser.BookmarkColumns.TITLE },
                    new int[] { android.R.id.text1}, 0);

            setListAdapter(mAdapter);

            // Start out with a progress indicator.
            setListShown(false);

            // Prepare the loader.  Either re-connect with an existing one,
            // or start a new one.
            getLoaderManager().initLoader(0, null, this);
        }

        //@Override 
        public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) 
        {
            // Place an action bar item for searching.
            MenuItem item = menu.add("Add Item");
            //item.setIcon(android.R.drawable.ic_menu_search);
            MenuItemCompat.setShowAsAction(item, MenuItemCompat.SHOW_AS_ACTION_ALWAYS);
        }

        @Override
        public boolean onOptionsItemSelected (MenuItem item)
        {
            ContentValues cv=new ContentValues();
            cv.put(Browser.BookmarkColumns.TITLE, "!AA " + System.currentTimeMillis());
            cv.put(Browser.BookmarkColumns.URL, "http://test/");
            cv.put(Browser.BookmarkColumns.BOOKMARK, 1);
            getActivity().getContentResolver().insert(Browser.BOOKMARKS_URI, cv);
            return true;
        }

       //columns to query
        static final String[] PROJECTION = new String[] { Browser.BookmarkColumns.TITLE };


        public Loader<Cursor> onCreateLoader(int id, Bundle args) 
        {
            Log.i(TAG, "onCreateLoader");

            return new CursorLoader(getActivity(), Browser.BOOKMARKS_URI,
                    PROJECTION, null, null,
                    Browser.BookmarkColumns.TITLE + " ASC");
        }

        public void onLoadFinished(Loader<Cursor> loader, Cursor data) 
        {
            Log.i(TAG, "onLoadFinished");

            // Swap the new cursor in.  (The framework will take care of closing the
            // old cursor once we return.)
            mAdapter.swapCursor(data);

            // The list should now be shown.
            if (isResumed()) 
                setListShown(true);
            else 
                setListShownNoAnimation(true);
        }

        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);
        }
    }

}