label value based on dropdown selection

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C#3.0

C#

ASP.NET

Hi All,

I am trying to make a order with the help of gridview where a dropdown select a item and label show rate of selected item.

and other two text box quantity inserted by user and amount calculated on item quantity and rate.

but when i am trying to bind these then all item and all rates of each item is polpulating in grid view when i am selecting item from dropdown no rate is change when ever i want if user selct other item then rate should be change.

following is my aspx code..

<asp:GridView ID="gridView1" runat="server" AutoGenerateColumns="False" AllowPaging="True" OnRowDataBound="gridView1_RowDataBound" PageSize="5">
            <Columns>
                <asp:TemplateField HeaderText="Product_Name">
                    <ItemTemplate>
                        <asp:DropDownList ID="DropDownList1" runat="server" DataValueField="product_id" DataTextField="product_name" Width="100px" OnSelectedIndexChanged="DropDownList1_SelectedindexChanged"> </asp:DropDownList>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Product_Rate">
                    <ItemTemplate>
                        <asp:Label ID="lblRate" runat="server" Text='<%#DataBinder.Eval(Container.DataItem,"Product_Rate") %>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Quantity">
                    <ItemTemplate>
                        <asp:TextBox ID="txtQuantity" runat="server" />
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Amount">
                    <ItemTemplate>
                        <asp:TextBox ID="txtAmount" runat="server" />
                    </ItemTemplate>
                </asp:TemplateField>
             </Columns>
          </asp:GridView>

asp.net c# code.

using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.Sql;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;
using System.Web.Security;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using Telerik.Web.UI;

namespace RadControlsWebApp1
{
    public partial class testtttttttttttttttt : System.Web.UI.Page
    {
        DataTable dt;
        DataRow dr; 

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
            fillgrid();
            createdatatable();
            }
        }
        protected void fillgrid()
        {
            SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings["connectionstring"].ToString());
            SqlCommand cmd = new SqlCommand("select product_name,product_rate from product_detail", con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds, "product_detail");
            gridView1.DataSource = ds;
            gridView1.DataBind();
        }

        protected void createdatatable()
        {
       dt = new DataTable();

       dt.Columns.Add("product_name");
       dt.Columns.Add("product_rate");
       dt.Columns.Add("product_Quantity");
       dt.Columns.Add("product_Amount");

        }


        protected void btnHome_Click(object sender, EventArgs e)
        {
            //Response.Redirect("Home.aspx");
        }
      

        protected void gridView1_RowDataBound(object sender, GridViewRowEventArgs e)
        {

            if (e.Row.RowType == DataControlRowType.DataRow)
            {
                SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings["connectionstring"].ToString());
                SqlCommand cmd = new SqlCommand("select product_id,product_name,product_rate from product_detail", con);
                SqlDataAdapter da = new SqlDataAdapter(cmd);
                DataSet ds = new DataSet();
                da.Fill(ds);
                DropDownList ddl = (DropDownList)e.Row.FindControl("DropDownList1");
                ddl.DataSource = ds;
                ddl.DataTextField = "product_name";
                ddl.DataValueField = "product_id";
                ddl.DataBind();
            }
          
        }
        protected void DropDownList1_SelectedindexChanged(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings["connectionstring"].ToString());
            SqlCommand cmd = new SqlCommand("select product_id,product_name,product_rate from product_detail", con);
            SqlDataReader reader;
            reader = cmd.ExecuteReader();
            if (reader.Read())
            { 
            }
          }
    }
}

i am unable to do how can i do that??

Thanks