Row Editing Two Datakey Pass to Querystring

String 1stquerystring=gridview.DataKeys[e.NewEditIndex].Values["Datakey1"].ToString();

String 2ndquerystring=gridview.DataKeys[e.NewEditIndex].Values["Datakey2"].ToString();

<asp:gridview id="GridView1" runat="server" autogeneratecolumns="false" datakeynames="tprice,tquantity" onselectedindexchanged="GridView1_SelectedIndexChanged" xmlns:asp="#unknown">
        <columns>
 <asp:commandfield showselectbutton="true" />
        </columns>
        </asp:gridview>

protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
  {
      string tprice2 = Server.HtmlDecode(GridView1.SelectedDataKey["tprice"].ToString());
      string tquantity1 = Server.HtmlDecode(GridView1.SelectedDataKey["tquantity"].ToString());
  }