使用AsyncTaskLoader动态载入SQLite数据

Andorid API Guides中有一章节ListView讲解了如何使用CursorLoader动态载入数据。但CursorLoader只支持Content Provider，实际上在很多小应用中都用不到Content Provider。我尝试继承CursorLoader的父类也就是AsyncTaskLoader实现了一个简单的动态载入SQLite数据的方案。如有不当之处希望指正。

NotesLoader继承AsyncTaskLoader

public class NotesLoader extends AsyncTaskLoader<Cursor> {
    private NotesDbAdapter notesDbAdapter;	//NotesDBAdapter可以在Android Example中找到，这里略作修改，以便支持多数据表的访问

    public NotesLoader(Context context, String tableName) {
        super(context);
        notesDbAdapter = new NotesDbAdapter(context, tableName);
    }

    @Override
    protected void onStartLoading() {
        Log.v("onStartLoading", "OK");
        forceLoad();	//强制加载
    }
    @Override
    public Cursor loadInBackground() {
        Log.v("loadInBackground","OK");
        notesDbAdapter.open();
        mCursor = notesDbAdapter.fetchAllNotes();
        return mCursor;
    }

    @Override
    protected void onStopLoading() {
        Log.v("onStopLoading","OK");
        notesDbAdapter.close();
    }
}

PlaceholderFragment接口LoaderManager，换成Activity也是一样的

public class PlaceholderFragment extends ListFragment
        implements LoaderManager.LoaderCallbacks<Cursor>{
    private Cursor mNotesCursor;
    private SimpleCursorAdapter notesAdapter=null;
    private int oldLoaderId;
    private int newLoaderId;

    public PlaceholderFragment() {    }

    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);

        // Create an array to specify the fields we want to display in the list (only TITLE)
        String[] from = new String[]{NotesDbAdapter.KEY_TITLE};

        // and an array of the fields we want to bind those fields to (in this case just text1)
        int[] to = new int[]{R.id.subject_date_text1};
        notesAdapter =
                new SimpleCursorAdapter(getActivity(), R.layout.row_subject_date, null, from, to, 0);
        setListAdapter(notesAdapter);
        return rootView;
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data)    {
        NotesUID note = new NotesUID();
        Bundle extras = null;
        if (data != null) {
            extras = data.getExtras();
        }
        try {
            if ({更换Cursor，对应在数据库中更换数据表}) {
                getLoaderManager().destroyLoader(oldLoaderId);
                getLoaderManager().initLoader(newLoaderId, null, this);
            } else if ({刷新Cursor}) {
                getLoaderManager().restartLoader(oldLoader,null,this);
            }
        } catch (Exception e) {
            Log.e("PlaceholderFragment onActivityResult","error:"+e.getMessage());
        }
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        if (mNotesCursor != null)
            mNotesCursor.close();
    }

    @Override
    // Called when a new Loader needs to be created
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        // Now create and return a CursorLoader that will take care of
        // creating a Cursor for the data being displayed.
        Log.v("onCreateLoader","OK");
        return new NotesLoader(getActivity(), {通过id找到数据表名});
    }

    @Override
        // Called when a previously created loader has finished loading
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        // 这里没有使用SwapCursor，而是使用了changeCursor，因为ChangeCursor比较明确老的cursor会被关闭，
        //SwapCursor由于不太清楚机制，不太敢用
        Log.v("onLoadFinished","OK");
        notesAdapter.changeCursor(data);
        mNotesCursor = data;
    }


    @Override
    // Called when a previously created loader is reset, making the data unavailable
    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.
        Log.v("onLoaderReset","OK");
        notesAdapter.changeCursor(null);
    }
}

NotesLoader继承AsyncTaskLoader