A thousand thanks.A new problem rise.I add the onclick function to the linkbutton as follows:
      function abc(isTaken,infoId){
         var index = $('#info_dg').datagrid('getRowIndex',infoId);
         $('#info_dg').datagrid('updateRow',{
            index: index,
            row: {
               isTaken : 1-isTaken
            }
         });
         $('#info_dg').datagrid('refreshRow',index);
      }
(linkbutton's text and icon depends on the isTaken).
After click,the text is correct but the linkbutton disapear.What shouldI do?

<th field="isTaken" width="100" align="center" data-options="
   formatter:takenfomatter
">taken</th>

function takenfomatter(isTaken,row,index){
   var returnStr = "<a href=\"javascript:void(0)\" class='easyui-linkbutton' iconCls=\"icon-add\" onclick=\"javascript:alert('easyui')\">easyui</a>"
        return returnStr;
}

When I turn out.println("true") to out.print("true"),it works,I don't know why.

My code is like this:
<input type="text" class="easyui-numberbox" name="candNum"
            data-options="
               min:0,
               max:99999,
               required:true,
               validType:{
                  length:[1,5],
                  remote:['info_validateCandNum.action','candNum']
               },
               delay:400,
               formatter:function(value){
                  var str = value.toString();
                  while(str.length<5){
                     str = '0'+str;
                  }
                  return str;
               }
            ">
the server side can get the param,and will return 'true' at last
 PrintWriter out = response.getWriter();
 out.println("true");
however,the numberbox is still in the invalid state.Can anyone solve my problem?

10 items/page,11 items in all,destroy the 11 item in the second page,the datagrid show blank instead of 10 items in the first page.

after checking mycode,I find my formatter function wrong because lacking
if(value==null){
 return ;
}
I'm so sorry for my careless.
I still have a question:How can I get a feedback after adding row in edatagrid mode?Can you give me a demo or some hints?

here is my code:
<th field="deptID" width="50" align="center"
   editor="{
      type:'validatebox',
      options:{
         required:true,
         formatter:function(value,row,index){
            var deptIDStr = value.toString();
            while(deptIDStr.length<3){
               deptIDStr = '0'+deptIDStr;
            }
            return deptIDStr;
         }
      }
   }">deptID</th>
   deptID is the idField,when I press the add Button,it doesn't work.

when I remove the formatter code,it works well.Please give me some hints