public string ToJson(ArrayList a, int colNumber)        

{             StringBuilder stringBuilder = new StringBuilder("{");          
 stringBuilder.Append("total: " + SurrondWithQuote(10) + ", ");          
 stringBuilder.Append("page: " + SurrondWithQuote(1) + ", ");          
 stringBuilder.Append("records: " + SurrondWithQuote(1) + ", ");            
stringBuilder.Append("  rows : [ ");          
 for (int i = 0; i < a.Count ; i++)          
 {                
string[] temp = a[i] as string[];                
stringBuilder.Append("{");
  stringBuilder.Append("id:" + SurrondWithQuote(i + 1) + ", ");                
stringBuilder.Append("cell:[ ");              
 for (int j = 0; j < colNumber; j++)                
{                    if (j + 1 != colNumber)                  
 {                        
stringBuilder.Append(SurrondWithQuote(temp[j]) + ", ");                    }                  
 else                       
 stringBuilder.Append(SurrondWithQuote(temp[j]));              
 }                

stringBuilder.Append(" ]");

                if (i == a.Count - 1)              
 {                    stringBuilder.Append(" }");                }              
 else                {                    stringBuilder.Append(" },");                }            
}            
stringBuilder.Append(" ]");          
 stringBuilder.Append(" }");          
 return stringBuilder.ToString();      
 }

I would you not recommend to use datatype as function. If was introduced in old versions of jqGrid. Now one should use better parameters like ajaxGridOptions. 

I find also a little strange, that your server page has extension aspx and not asmx (web service), svc (WCF service) or using ASP.NET MVC with no extension for the URL providing JSON data. Which technology  you use on the server side to produce the JSON output? Wich version of .NET and which version of the Visual Studio you use?

If you gives more information about your server part and the jqGrid version used I'll try to post you some links with the corresponding examples.

Regards
Oleg 

in fact , I've tried this, used " jQuery("#productGridView").setGridParam({ datatype: getProducts});" 
to reset the datetype. but it seems that does not work on my computer, server side never receive the 
postback, and the jqgrid just redraw itself , each time, at the bottom , it add the icon for "search" and "refresh", 
maybe there is a conflict of JS ? 

here is my code, could you please check it and tell me where is my problem ?  Thanks a lot  

function getProducts() {            
$.ajax({                
url: "Test.aspx",              
data: jsonData(),                  
dataType: "json",                
type: "POST",                
success: successFunction          
 });        

}

function dataBindToGrid() {

    jQuery("#productGridView").jqGrid({

    datatype: getProducts,

    colNames: ['TestCol1', 'TestCol2', 'TestCol3'],

    colModel: [{ name: 'TestCol1', index: 'TestCol1', width: 200, align: 'left', resizable: true },{ name: 'TestCol2', index: 'TestCol2', width: 200, align: 'left', resizable: true },{ name: 'TestCol3', index: 'TestCol3', width: 200, align: 'left', resizable: true }],

    rowNum: 10,

    autowidth: true,

    rownumbers: true,

    rowList: [5, 10, 20, 50, 100],

    sortname: 'TestCol1',

    pager: jQuery('#pageNavigation'),

    sortorder: "desc",

    viewrecords: true,

    multiselect: true,

    height: 50,

    loadonce: true,

    gridComplete: function () {

           $("#productGridView").setGridParam({ datatype: 'local' });

         }

    });

    jQuery("#productGridView").jqGrid('navGrid','#pageNavigation',  
                               {add:false,edit:false,del:false});

}

jQuery(document).ready(function () {

    jQuery("#testButton1").click(function () {

          jQuery("#productGridView").setGridParam({ datatype: getProducts});

          dataBindToGrid();

});

});

Look at this old answer. You should just reset the datatype to "local" before reloading of the grid.

Regards
Oleg 

I'm a beginner in jqgrid . when I tried to use it, I've met this problem :

 I set loadonce= true, and set datatype="local",  the grid is OK on the page .
and now I need to research the data from the server side and reload the grid ,
I tried some methods from internet , but doesn't work, or maybe I could not use 
"loadonce = true" at this time ?  

please help ....