Making changes to a pre-populated textbox - asp.net

Question

I have the following webform with textboxes that are pre-populated on page load:
<%# Page Title="" Language="VB" MasterPageFile="~/default.master" AutoEventWireup="true" CodeFile="admin.aspx.vb" Inherits="admin" Theme="G2M" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<form id="form1" Runat="Server">
<label>Username: </label>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<br />
<label>Password: </label>
<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
<br />
<label>Product Type: </label>
<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
<br />
<label>SMTP Default Only: </label>
<asp:TextBox ID="TextBox4" runat="server"></asp:TextBox>
<br />
<label>Logo: </label>
<asp:TextBox ID="TextBox5" runat="server"></asp:TextBox>
<br />
<asp:Button ID="submit" Text="Submit changes" runat="server" OnClick="SubmitChanges" />
</form>
</asp:Content>
And the codebehind is as follows:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim xmlDoc As New XmlDocument
xmlDoc.Load(Server.MapPath("~/XML_Config/Config.xml"))
Dim configValues As XMLParser = New XMLParser(xmlDoc) ''Instantiate the XMLParser
''Populate textboxes with XML data
TextBox1.Text = configValues.UserName
TextBox2.Text = configValues.Password
TextBox3.Text = configValues.ProductType
TextBox4.Text = configValues.SMTPDefaultOnly
TextBox5.Text = configValues.Logo
End Sub
Public Sub SubmitChanges(ByVal sender As Object, ByVal e As System.EventArgs)
Dim xmlDoc As New XmlDocument
xmlDoc.Load(Server.MapPath("~/XML_Config/Config.xml"))
Dim configValues As XMLParser = New XMLParser(xmlDoc) ''Instantiate the XMLParser
configValues.SMTPDefaultOnly = TextBox4.Text
End Sub
All I'm trying to do is make the values editable so when the form is presented to the user, they can change the values and submit them back to the file. My problem is that when the SubmitChanges function is called, even though I change the value of the textbox, it is still the same. How do I pass a new value, typed into thetextbox, to the function?

Answer 1

Enclose your setter in If Not ispostback in that page load. It's overwriting the boxes.