Sorting gridview - can't find column - asp.net

Question

Relative newbie here. Discovered that I have to write an event handler to handle sorting of my data from an objectdatasource. Found a lot of references to code like what's below, but when the code runs I get the message "Cannot find column xxx" where xxx is the name of the column I'm trying to sort on.
I've verified that e.SortExpression is returning the proper column name, but the problem appears to be in the 2nd line below, where I try to create a datatable (dt) from the GridView1.Datasource. The value of dt after this statement is 'nothing', so the rest of the code fails.
Also, I'm listing most of the gridview definition in case that's helpful.
Protected Sub GridView1_Sorting(sender As Object, e As GridViewSortEventArgs) Handles GridView1.Sorting
Dim dt As Data.DataTable = New Data.DataTable(GridView1.DataSource)
If Not dt Is Nothing Then
dt.DefaultView.Sort = e.SortExpression
GridView1.DataSource = dt
GridView1.DataBind()
End If
End Sub
ASPX snippet:
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
DataSourceID="ObjectDataSource1" CellPadding="4"
EmptyDataText="No records found for your search" ForeColor="#333333"
GridLines="None" Width="930px" BorderColor="#CCCCCC" Font-Size="12px" AllowSorting="True">
<AlternatingRowStyle BackColor="White" ForeColor="#284775" />
<Columns>
<asp:BoundField DataField="CustName" HeaderText="CustName"
SortExpression="CustName" />
<asp:BoundField DataField="CustType" HeaderText="CustType"
SortExpression="CustType" HeaderStyle-HorizontalAlign="Center" ItemStyle-HorizontalAlign="Center" />
<asp:TemplateField HeaderText="Address" SortExpression="Addr1">
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("Addr1") %>'></asp:Label>
</ItemTemplate>
<EditItemTemplate>
<asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("Addr1") %>'></asp:TextBox>
</EditItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="Phone" HeaderText="Phone" SortExpression="Phone" />
<asp:BoundField DataField="ContactName" HeaderText="ContactName"
SortExpression="ContactName" />
<asp:BoundField DataField="LastContactDate" HeaderText="LastContact" SortExpression="LastContactDate" dataformatstring="{0:d}" />
<asp:BoundField DataField="CustSince" HeaderText="CustSince"
SortExpression="CustSince" dataformatstring="{0:MM/dd/yyyy}" />
<asp:BoundField DataField="Status" HeaderText="Status"
SortExpression="Status" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center" />
<asp:BoundField DataField="Source" HeaderText="Source"
SortExpression="Source" />
<asp:BoundField DataField="RelMgr" HeaderText="RelMgr"
SortExpression="RelMgr" />
<asp:TemplateField HeaderText="RelMgrInfo">
<ItemTemplate>
<asp:HyperLink ID="RelMgrEmailLink" runat="server" NavigateUrl='<%#Eval("RelMgrEmail", "mailto:{0}")%>' Text='<%# Eval("RelMgrEmail") + "<br>" + Eval("RelMgrPhone")%> '> </asp:HyperLink>
</ItemTemplate>
</asp:TemplateField>
</Columns>
Thanks!

Answer 1

You don't have to handle the sorting event if you work with the ObjectDataSource. Instead, set the SortParameterName to a string (like "OrderBy") and augment your business method signature that ObjectDataSource uses to retrieve data with this parameter:
public IEnumerable<Whatever> Retrieve( string OrderBy, ... other arguments ) ...
The grid will pass the parameter value to the ODS and then ODS will pass it to your method.