如何使用CursorAdapter和LoaderCallbacks在片段中实现ContentObserver？

Question

我在a CursorAdapter中使用a ListFragment来加载和显示注释列表.

public class CommentsFragment extends ListFragment implements LoaderCallbacks<Cursor> {

    protected Activity mActivity;
    protected CursorAdapter mAdapter;

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        mActivity = getActivity();
        mAdapter = new CommentsCursorAdapter(mActivity, null, 0);
        setListAdapter(mAdapter);
        mActivity.getContentResolver().registerContentObserver(CustomContract.Comments.CONTENT_URI, false, new CommentsObserver());
        getLoaderManager().initLoader(0, null, this);
    }

    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle extras) {
        Uri uri = CustomContract.Comments.CONTENT_URI;
        return new CursorLoader(mActivity, uri, null, null, null, null);
    }

    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
        mAdapter.swapCursor(cursor);
    }

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        mAdapter.swapCursor(null);
    }

    protected class CommentsObserver extends ContentObserver {

        public CommentsObserver() {
            super(new Handler());
        }

        @Override
        public void onChange(boolean selfChange) {
            super.onChange(selfChange);
            // TODO Trigger a reload.
        }

    }
}

在我notifyChange()为插入操作添加的关联ContentProvider中.

@Override
public Uri insert(Uri uri, ContentValues values) {
    final SQLiteDatabase db = mOpenHelper.getWritableDatabase();
    int match = sUriMatcher.match(uri);
    switch (match) {
        case COMMENTS: {
            long id = db.insert(DatabaseProperties.TABLE_NAME_COMMENTS, null, values);
            Uri itemUri = ContentUris.withAppendedId(uri, id);
            // FIXME Which one is right?
            getContext().getContentResolver().notifyChange(itemUri, null);
            getContext().getContentResolver().notifyChange(uri, null);
            return itemUri;
        }
        default: {
            throw new UnsupportedOperationException("Unknown URI: " + uri);
        }
    }
}

问题:

1. 是否可以作为观察者参数传递null给它notifyChange()？如果没有,我应该通过什么对象？
2. 我应该通过uri还是itemUri进去notifyChange()？为什么？
3. 我需要用什么方法CommentsObserver#onChange()来更新评论列表？
4. 有没有我可以实现的接口ListFragment而不是内部类实例ContentObserver？
5. 我只是new Handler()在构造函数中实例化一个CommentsObserver.这对我来说似乎不正确 - 请解释一下.

Answer 1

SqlCursor已经有内部ContentObserver,因为你正在使用这个Cursor实现,所以不需要自己的ContentObserver实现.

为方便使用,您可以添加:

class MyContentProvider extends ContentProvider{
  //rest implementation goes here
  @Override
  public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
    Cursor cursor = null;
    //check uri, select table name based on uri, etc ...
    cursor = db.query(/*.....*/);
    //add this line:
    cursor.setNotificationUri(getContext().getContentResolver(), uri);
    //before you return cursor
    return cursor;
  }
  @Override
  public Uri insert(Uri uri, ContentValues values) {
     /* ... */
       //you can notify only "dir" uri and is should be enough
       getContext().getContentResolver().notifyChange(uri, null);
       return itemUri;
     /* ... */
  }
  //rest of implementation goes here
}

在此之后,CursorLoader内部实现将负责重新加载/刷新数据......