อยากจะอัพเดตก็ต่อเมื่อกดปุ่มโดยใช้ข้อมูลจากกริดวิว...เมื่อผมกดไปแล้วอยากจะให้ข้อมูลตรงส่วนจำนวนไปอัพเดตของข้อมูลสินค้าอ่ะครับ

Protected Sub _btnClearCart_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles _btnClearCart.Click
        Dim now As Date = Date.Now.ToShortDateString

        Dim a As CheckBox
        Dim c As Label
        Dim i As Integer

        For i = 0 To GridView1.Rows.Count - 1

            a = GridView1.Rows(i).FindControl("checkid") <--- ขึ้นตรงนี้
            c = GridView1.Rows(i).FindControl("proid")


            If a.Checked = True Then
                Dim sel As New SqlDataAdapter("select num from product,cart where cart.pro_id='" & c.Text & "' ", con)
                Dim sel1 As New DataSet
                sel.Fill(sel1, "up")

                Dim sql As String = "delete from cart where username='" & Session("user") & "' and buy='" & now & "' "
                Dim up As New SqlCommand("update product set pro_total=pro_total+" & sel1.Tables("up").Rows(i)("num") & " where pro_id='" & c.Text & "' ", con)
                Dim dr As SqlDataReader
                con.Open()
                Dim cmd As New SqlCommand(sql, con)
                cmd.ExecuteNonQuery()
                up.ExecuteNonQuery()
                dr = cmd.ExecuteReader
                GridView1.DataSource = dr
                GridView1.DataBind()
                con.Close()
                Session("s") = Session("s") - _lblOrderTotal.Text
            End If
        Next

        _lblOrderTotal.Visible = False
        Label9.Visible = False
        Label8.Visible = True

    End Sub