如何更新通过SimpleCursorAdapter从数据库查询数据的listview?

时间:2012-01-15 09:48:39

标签: android cursor simplecursoradapter

我想用SimpleCursorAdapter显示列表视图中从数据库查询的项目。 例如,数据库中可能有20,000个项目。我想只加载100项(_id:1-100)查询而不是加载所有项目,当在listview的末尾滚动时,加载另外100项(_id:101-200)查询,如何实现它?欢迎任何建议,谢谢。

相关代码如下:

protected void onCreate(Bundle savedInstanceState) {
    mCursor = managedQuery(CONTENT_URI, PROJECTION, null, null, "_id DESC");
    mAdapter = new SimpleCursorAdapter(this,R.layout.list_content,  mCursor, keys,  values);
    setListAdapter(mAdapter);
}

在我定义的列表视图中,我想通过查询数据库加载更多项目。

public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) 
{
    int lastItem = firstVisibleItem + visibleItemCount - 1;

    if (mListAdapter != null) {
        if ((lastItem == mListAdapter.getCount()-1) && (mRefreshState != REFRESHING)) {
            mFooterView.setVisibility(View.VISIBLE);
            mRefreshState = REFRESHING;
            new Handler().postDelayed(new Runnable() {  
                public void run() {  
                    //execute the task ,  i want to load more items by query database
                    RefreshListView(LOADING_STORED_INFO);                                           
                }  
             }, DEFAULT_DELAY_TIMER);           
        }
    }
}

在AsyncTask加载数据中,我执行查询操作。

    protected Integer doInBackground(Integer... params)
    { 
        Uri uri = ContentUris.withAppendedId(CONTENT_URI, mCursor.getInt(0)-1);
        cursor = managedQuery(uri, PROJECTION, null, null, "_id DESC");
        return (0 == params[0]) ? 1 : 0;
    }

    @Override
    protected void onPostExecute(Integer result)
    {
        mAdapter.changeCursor(cursor);//is this OK?
        mAdapter.notifyDataSetChanged();
        /*
        if (1 == result)
        {
            mListView.setSelection(1);
        }
        else
        {
            mListView.setSelection(mCount-1);               
        }*/
        // Call onRefreshComplete when the list has been refreshed.
        mListView.onRefreshComplete(result); 
        super.onPostExecute(result);
    } 

1 个答案:

答案 0 :(得分:2)

以这种方式在SQL查询中使用LIMIT语句:

SELECT your_column FROM your_table ORDER BY your_order LIMIT limit_skip, limit_count

然后,您可以使用OnScrollListener检索第一个可见单元格的索引和可见单元格的数量,以便您可以连贯地增加limit_skiplimit_count

而不是通用AsyncTask使用CursorLoader并实施LoaderManager.LoaderCallbacks<Cursor>,如下所示:

public Loader<Cursor> onCreateLoader(int id, Bundle args){
    String orderBy = "_id DESC"
    if(args != null){
        orderBy += " LIMIT " + args.getInt("LIMIT_SKIP") + "," + args.getInt("LIMIT_COUNT");
    }

    return new CursorLoader(this /*context*/, CONTENT_URI, PROJECTION, null, null, orderBy);
}

public void onLoadFinished(Loader<Cursor> loader, Cursor data){
    listAdapter.swapCursor(data);
}

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

然后,在onCreate()中,将null作为cursor传递给new SimpleCursorAdapter()并以这种方式创建CursorLoader

getLoaderManager().initLoader(0, null, this /*LoaderCallbacks<Cursor>*/);

然后,在onScroll()中,每次以这种方式重置加载器:

Bundle args = new Bundle();
args.putInt("LIMIT_SKIP", limit_skip_value);
args.putInt("LIMIT_COUNT", limit_count_value);
getLoaderManager().restartLoader(0, args, this /*LoaderCallbacks<Cursor>*/);