Update met gegevens uit textbox

<%@ Page Language="VB" MasterPageFile="~/layout.master" AutoEventWireup="false" CodeFile="product_bewerken.aspx.vb" Inherits="product_bewerken" title="Untitled Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="contentplaceholder" Runat="Server">
<form runat="server">
    <table style="width: 100%">
        <tr>
            <td colspan="2">
                Je kunt hieronder het product bewerken
                <asp:Label ID="lblTest" runat="server" Style="z-index: 100; left: 0px; position: absolute;
                    top: 0px"></asp:Label>
            </td>
        </tr>
        <tr>
            <td style="width: 209px; height: 69px;">
                <asp:Label ID="lblCategorie" runat="server" Text="Categorie:"></asp:Label></td>
            <td style="height: 69px">
                <asp:DropDownList ID="cboCategorie" runat="server" DataSourceID="dtsCategorieen"
                    DataTextField="cat_naam" DataValueField="cat_id">
                </asp:DropDownList><asp:SqlDataSource ID="dtsCategorieen" runat="server" ConnectionString="<%$ ConnectionStrings:conGIP %>"
                    SelectCommand="SELECT * FROM [tblCategorieen]"></asp:SqlDataSource>
            </td>
        </tr>
        <tr>
            <td style="width: 209px; height: 21px">
                <asp:Label ID="lblNaam" runat="server" Text="Naam:"></asp:Label></td>
            <td style="height: 21px">
                <asp:TextBox ID="txtNaam" runat="server"></asp:TextBox></td>
        </tr>
        <tr>
            <td style="width: 209px; height: 21px">
                <asp:Label ID="lblInfo" runat="server" Text="Info:"></asp:Label></td>
            <td style="height: 21px">
                <asp:TextBox ID="txtInfo" runat="server"></asp:TextBox></td>
        </tr>
        <tr>
            <td style="width: 209px; height: 21px">
                <asp:Label ID="lblPrijs" runat="server" Text="Prijs:"></asp:Label></td>
            <td style="height: 21px">
                <asp:TextBox ID="txtPrijs" runat="server"></asp:TextBox></td>
        </tr>
        <tr>
            <td colspan="2" style="height: 26px">
                <asp:Button ID="cmdBewerken" runat="server" Text="Bewerken" /><br />
                <asp:Label ID="lblBewerken" runat="server"></asp:Label></td>
        </tr>
        <tr>
            <td colspan="2" style="height: 26px">
            </td>
        </tr>
    </table>
   </form>
</asp:Content>

<%@ Page Language="VB" MasterPageFile="~/layout.master" AutoEventWireup="false" CodeFile="product_bewerken.aspx.vb" Inherits="product_bewerken" title="Untitled Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="contentplaceholder" Runat="Server">
<form runat="server">
    <table style="width: 100%">
        <tr>
            <td colspan="2">
                Je kunt hieronder het product bewerken
                <asp:Label ID="lblTest" runat="server" Style="z-index: 100; left: 0px; position: absolute;
                    top: 0px"></asp:Label>
            </td>
        </tr>
        <tr>
            <td style="width: 209px; height: 69px;">
                <asp:Label ID="lblCategorie" runat="server" Text="Categorie:"></asp:Label></td>
            <td style="height: 69px">
                <asp:DropDownList ID="cboCategorie" runat="server" DataSourceID="dtsCategorieen"
                    DataTextField="cat_naam" DataValueField="cat_id">
                </asp:DropDownList><asp:SqlDataSource ID="dtsCategorieen" runat="server" ConnectionString="<%$ ConnectionStrings:conGIP %>"
                    SelectCommand="SELECT * FROM [tblCategorieen]"></asp:SqlDataSource>
            </td>
        </tr>
        <tr>
            <td style="width: 209px; height: 21px">
                <asp:Label ID="lblNaam" runat="server" Text="Naam:"></asp:Label></td>
            <td style="height: 21px">
                <asp:TextBox ID="txtNaam" runat="server"></asp:TextBox></td>
        </tr>
        <tr>
            <td style="width: 209px; height: 21px">
                <asp:Label ID="lblInfo" runat="server" Text="Info:"></asp:Label></td>
            <td style="height: 21px">
                <asp:TextBox ID="txtInfo" runat="server"></asp:TextBox></td>
        </tr>
        <tr>
            <td style="width: 209px; height: 21px">
                <asp:Label ID="lblPrijs" runat="server" Text="Prijs:"></asp:Label></td>
            <td style="height: 21px">
                <asp:TextBox ID="txtPrijs" runat="server"></asp:TextBox></td>
        </tr>
        <tr>
            <td colspan="2" style="height: 26px">
                <asp:Button ID="cmdBewerken" runat="server" Text="Bewerken" /><br />
                <asp:Label ID="lblBewerken" runat="server"></asp:Label></td>
        </tr>
        <tr>
            <td colspan="2" style="height: 26px">
            </td>
        </tr>
    </table>
   </form>
</asp:Content>

Protected Sub cmdBewerken_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmdBewerken.Click
        Dim cnnConnectie As New SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings("conGIP").ToString())
        Dim cmdWijzigen As New SqlCommand
        cmdWijzigen.Connection = cnnConnectie
        cmdWijzigen.CommandText = "UPDATE tblProducten SET prod_naam='" & txtNaam.Text & "' WHERE prod_id='" & strProd & "'"
        Dim up As Object
        cnnConnectie.Open()
        Try
            up = cmdWijzigen.ExecuteNonQuery()
            lblBewerken.Text = "Product (" & txtNaam.Text & ") is bewerkt!"
        Catch ex As Exception
            lblBewerken.Text = "Error:" & ex.Message
        Finally
            cnnConnectie.Close()
        End Try
    End Sub

Protected Sub cmdBewerken_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmdBewerken.Click
        Dim cnnConnectie As New SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings("conGIP").ToString())
        Dim cmdWijzigen As New SqlCommand
        cmdWijzigen.Connection = cnnConnectie
        cmdWijzigen.CommandText = "UPDATE tblProducten SET prod_naam='" & txtNaam.Text & "' WHERE prod_id='" & strProd & "'"
        Dim up As Object
        cnnConnectie.Open()
        Try
            up = cmdWijzigen.ExecuteNonQuery()
            lblBewerken.Text = "Product (" & txtNaam.Text & ") is bewerkt!"
        Catch ex As Exception
            lblBewerken.Text = "Error:" & ex.Message
        Finally
            cnnConnectie.Close()
        End Try
    End Sub