Selected row Save problem in parent Grid

protected void Page_Load(object sender, EventArgs e)
   {
       if (!IsPostBack)
       {
           SqlConnection con = new SqlConnection(@"Data Source=IT-DEV2\SQLEXPRESS;Initial Catalog=test;Integrated Security=True");
           string statment = "select item_code, Item_name, brand, size, section, price, Material, Qty, tax, tt  from Items ";
           SqlDataAdapter da = new SqlDataAdapter(statment, con);
           DataSet ds = new DataSet();
           da.Fill(ds);
           GridView1.DataSource = ds.Tables[0];
           GridView1.DataBind();
       }
   }
   protected void GridView1_SelectedIndexChanging(object sender, GridViewSelectEventArgs e)
   {
       string  v1 = GridView1.Rows[e.NewSelectedIndex].Cells[1].Text;
       string v2 = GridView1.Rows[e.NewSelectedIndex].Cells[1].Text;
       string v3 = GridView1.Rows[e.NewSelectedIndex].Cells[1].Text;
       string v4 = GridView1.Rows[e.NewSelectedIndex].Cells[1].Text;
       SqlConnection con = new SqlConnection(@"Data Source=IT-DEV2\SQLEXPRESS;Initial Catalog=test;Integrated Security=True");
       con.Open();
       string statment = string.Format("insert into Items (Item_name, brand, size, section) values ('{0}' ,' {1}' , {2} , '{3}' )", v1,v2,Convert.ToInt32( v3),v4);
         SqlCommand cmd = new SqlCommand(statment,con);
       cmd.CommandType =  CommandType.Text;
       cmd.ExecuteNonQuery();
       cmd.Dispose();
       con.Close();

   }

<div>
       <asp:GridView ID="GridView1" runat="server"
           onselectedindexchanging="GridView1_SelectedIndexChanging">
           <Columns>
               <asp:CommandField ShowSelectButton="True" />
           </Columns>
       </asp:GridView>
   </div>