How to Change SQLDatasource Parameter on button press - asp.net

Question

I have a Gridview which is populating with entries fine.
What i need to do is enable it, so that when a string is entered within the textbox, it changes the SQLDatasource parameter to search for entries that match.
So this is the ASPx file that is being used.
<%# Page Language="vb" AutoEventWireup="True" CodeBehind="test.aspx.vb" MasterPageFile="~/Site1.Master"%>
<asp:Content ID="content" runat="server" ContentPlaceHolderID="Content">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<span class="country"></span>
<div align="right">
<asp:TextBox runat="server" ID="textbox1"></asp:TextBox>
<asp:Button runat="server" Text="Search" ID="Button1" OnClientClick="Button1_click" PostBackUrl="~/test.aspx" />
</div>
<br />
<br />
<div align="center">
<asp:UpdatePanel runat="server" ID="updatepanel">
<ContentTemplate>
<asp:SqlDataSource runat="server" ID="datab" SelectCommand="SELECT * FROM [TEST] where [unit]=#unit" ConnectionString="<%$ ConnectionStrings:Con %>" ProviderName="<%$ ConnectionStrings:Con.ProviderName %>">
<SelectParameters>
<asp:Parameter DefaultValue="UK" Name="unit" Type="String" />
</SelectParameters>
</asp:SqlDataSource>
<asp:GridView ID="View" DataSourceID="datab" runat="server" CssClass="table" AllowSorting="True" AutoGenerateColumns="True" DataKeyNames="Id">
</asp:GridView>
</ContentTemplate>
</asp:UpdatePanel>
</div>
</asp:Content>
The above works absolutley fine, I can change the parameter manually, and it will work. However i cannot get it to update from user submission.
Backfile:
Public Class test
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim unit As String = textbox1.Text
datab.UpdateParameters("Unit").DefaultValue = unit
updatepanel.Update()
End Sub
End Class
I'm guessing that i am doing something wrong when referrencing the code behind page, as the page seems to refresh when i press the button.
Any help is appreciated.
******Edit********
I have tried to use the following code in the behind file, however it does not display anything on the actual page now.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim DS As SqlDataSource = New SqlDataSource
Dim con As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\local\test.accdb"
Dim sc As String = "SELECT * FROM [TEST] where [unit]=#unit"
DS.ID = "datab"
DS.ConnectionString = con
DS.SelectCommand = sc
DS.SelectParameters("Unit").DefaultValue = "UK"
View.DataSource = datab
View.DataBind()
End Sub