c# 转json EXTJS grid

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Text;

public partial class admin_json_json_grid : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
         
            int pageSize = 10;
            int start = 0;
            if (!string.IsNullOrEmpty(Request["limit"]))
            {
                pageSize = int.Parse(Request["limit"]);
                start = int.Parse(Request["start"]);
            }
           
           string sqlstr = "select hca_art_id,hca_art_title,hca_art_author,hca_art_ComputerName,hca_art_date from hca_art";
           Response.Write(jsongrid(DbHelperSQL.Query(sqlstr), start, pageSize));

        }

        public static string jsongrid(DataSet ds, int start, int pageSize)
        {

            StringBuilder json = new StringBuilder();
            foreach (DataTable dt in ds.Tables)
            {
                json.Append("{");
                json.Append("\"totalCount");
                json.Append("\":");
                json.Append(ds.Tables[0].Rows.Count);
                json.Append(",");
                json.Append("\"data");
                json.Append("\":[");
                int itemCount = (start + pageSize) > ds.Tables[0].Rows.Count ? ds.Tables[0].Rows.Count : (start + pageSize);
                for (int i = start; i < itemCount; i++)
                {
                    json.Append("{");
                    for (int j = 0; j < dt.Columns.Count; j++)
                    {
                        json.Append("\"");
                        json.Append(dt.Columns[j].ColumnName);
                        json.Append("\":\"");
                        json.Append(dt.Rows[i][j].ToString());
                        json.Append("\",");
                    }
                    json.Remove(json.Length - 1, 1);
                    json.Append("},");
                }
                json.Remove(json.Length - 1, 1);
                json.Append("]");
                json.Append("}");
            }
            return json.ToString();
        }


 
     
    }