easyui的datagrid对单列排序时onsortColumn事件如何触发？

我设置了sortable:'true'，remoteSort: false，但是排序时并没有触发onsortColumn，而是客户端直接完成了排序，请问还需要哪些设置？

[code="java"]
<!DOCTYPE html>



Basic DataGrid - jQuery EasyUI Demo





<br> function alertColumn(sort,order){<br> alert(sort+&#39;-&#39;+order);<br> }<br>


Basic DataGrid




The DataGrid is created from markup, no JavaScript code needed.


<table class="easyui-datagrid" title="Basic DataGrid" style="width:700px;height:250px"
        data-options="singleSelect:true,collapsible:true,url:'../datagrid/datagrid_data1.json',onSortColumn:alertColumn">
    <thead>
        <tr>
            <th data-options="field:'itemid',width:80">Item ID</th>
            <th data-options="field:'productid',width:100,sortable:true">Product</th>
            <th data-options="field:'listprice',width:80,align:'right'">List Price</th>
            <th data-options="field:'unitcost',width:80,align:'right'">Unit Cost</th>
            <th data-options="field:'attr1',width:250">Attribute</th>
            <th data-options="field:'status',width:60,align:'center'">Status</th>
        </tr>
    </thead>
</table>



[/code]