Try this code:
<table class="easyui-datagrid" title="DataGrid" style="width:400px;height:250px" data-options="
singleSelect:true,
cls:'mydatagrid',
dropAccept:'.mydatagrid tr.datagrid-row',
data:data,
onLoadSuccess:function(){
$(this).datagrid('enableDnd');
}
">
<thead>
<tr>
<th data-options="field:'itemid',width:80">Item ID</th>
<th data-options="field:'productid',width:100">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>