Filling GridView Based on DropDownList selected Value (vb.net) - asp.net

Question

I have a drop down list that has inventory material groups, and I would like there to be a way that when I select a different group, the grid view loads the materials for that group. I'm a little confused on how to accomplish this...
ASPX
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:Design_Construction_V2ConnectionString %>" ProviderName="<%$ ConnectionStrings:Design_Construction_V2ConnectionString.ProviderName %>" SelectCommand="SELECT [UnitPriceInfo], [groupNumber], [itemDescription], [CrossTieType], [AFEFunctionCode], [AFECode], [unitType], [unitPrice] FROM [itemsList_]" FilterExpression="groupNumber = {0}">
<FilterParameters>
<asp:ControlParameter Name="groupNumber" ControlID="ddlMaterials" PropertyName="SelectedValue" Type="Int32" DefaultValue="" />
</FilterParameters>
</asp:SqlDataSource>
<asp:DropDownList runat="server" ID="ddlMaterials"></asp:DropDownList>
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1" EmptyDataText="There are no data records to display.">
<Columns>
<asp:BoundField DataField="UnitPriceInfo" HeaderText="UnitPriceInfo" SortExpression="UnitPriceInfo" />
<asp:BoundField DataField="groupNumber" HeaderText="groupNumber" SortExpression="groupNumber" />
<asp:BoundField DataField="itemDescription" HeaderText="itemDescription" SortExpression="itemDescription" />
<asp:BoundField DataField="CrossTieType" HeaderText="CrossTieType" SortExpression="CrossTieType" />
<asp:BoundField DataField="AFEFunctionCode" HeaderText="AFEFunctionCode" SortExpression="AFEFunctionCode" />
<asp:BoundField DataField="AFECode" HeaderText="AFECode" SortExpression="AFECode" />
<asp:BoundField DataField="unitType" HeaderText="unitType" SortExpression="unitType" />
<asp:BoundField DataField="unitPrice" HeaderText="unitPrice" SortExpression="unitPrice" />
</Columns>
</asp:GridView>
CODEBEHIND
Private Sub ddlMaterials_Load(sender As Object, e As EventArgs) Handles ddlMaterials.Load
If Not IsPostBack Then
Dim db As New DesignConstructionDataContext
Dim materials = (From m In db.Estimate_Groups
Where (m.BigGroup = "Materials")
Select m.groupName)
ddlMaterials.DataSource = materials
ddlMaterials.DataBind()
End If
End Sub
Private Sub ddlMaterials_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ddlMaterials.SelectedIndexChanged
End Sub

Answer 1

Change FilterParameters to SelectParameters. In where clause use this - where groupNumber = #groupNumber. So changed aspx will be like following.
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:Design_Construction_V2ConnectionString %>" ProviderName="<%$ ConnectionStrings:Design_Construction_V2ConnectionString.ProviderName %>" SelectCommand="SELECT [UnitPriceInfo], [groupNumber], [itemDescription], [CrossTieType], [AFEFunctionCode], [AFECode], [unitType], [unitPrice] FROM [itemsList_] where groupNumber = #groupNumber">
<SelectParameters>
<asp:ControlParameter Name="groupNumber" ControlID="ddlMaterials" PropertyName="SelectedValue" Type="Int32" DefaultValue="" />
</SelectParameters>
</asp:SqlDataSource>