"input string format" error binding DetailView to Gridview clicked row - webforms

Question

I'm reacquainting myself with Web Forms programming, using the ubiquitous Northwind database as a backing db for my project. I'm following a simple design pattern for displaying Customers, Products, etc., by displaying a databound gridview at the top of a page, then using the selected row of the gridview to display single item details in a DetailsView. This has been working perfectly well until, for some reason, I started working with a particular table (Suppliers). I am getting the following error:
The display of the Suppliers Gridview itself works perfectly until I add the DetailsView code. My Gridview-related code is as follows:
<asp:GridView ID="gvSuppliers" class="table table-bordered table-condensed table-responsive table-hover" runat="server" AutoGenerateColumns="False"
autogenerateselectbutton="True" AllowPaging="True" DataSourceID="dsSuppliersObjectSource" DataKeyNames="SupplierID" >
<columns>
<asp:BoundField DataField="SupplierID" HeaderText="SupplierID" SortExpression="SupplierID" />
<asp:BoundField DataField="CompanyName" HeaderText="CompanyName" SortExpression="CompanyName" />
<asp:BoundField DataField="ContactName" HeaderText="ContactName" SortExpression="ContactName" />
<asp:BoundField DataField="ContactTitle" HeaderText="ContactTitle" SortExpression="ContactTitle" />
<asp:BoundField DataField="Address" HeaderText="Address" SortExpression="Address" />
<asp:BoundField DataField="City" HeaderText="City" SortExpression="City" />
<asp:BoundField DataField="Region" HeaderText="Region" SortExpression="Region" />
<asp:BoundField DataField="PostalCode" HeaderText="PostalCode" SortExpression="PostalCode" />
<asp:BoundField DataField="Country" HeaderText="Country" SortExpression="Country" />
<asp:BoundField DataField="Phone" HeaderText="Phone" SortExpression="Phone" />
<asp:BoundField DataField="Fax" HeaderText="Fax" SortExpression="Fax" />
<asp:BoundField DataField="HomePage" HeaderText="HomePage" SortExpression="HomePage" />
</columns>
</asp:GridView>
<asp:ObjectDataSource ID="dsSuppliersObjectSource" runat="server" EnablePaging="True" SelectMethod="GetSuppliers"
SelectCountMethod="GetSuppliersCount" TypeName="Unknown_Web_Forms.SupplierDS" MaximumRowsParameterName="maxRows"
StartRowIndexParameterName="startIndex">
</asp:ObjectDataSource>
Note I am using an object data source; the relevant code, a method named "GetSuppliers", is a simple LINQ query, which, again, is working just fine:
public List<Supplier> GetSuppliers(int startIndex, int maxRows)
{
using (NorthwindEntities entities = new NorthwindEntities())
{
return (from supplier in entities.Suppliers
select supplier)
.OrderBy(supplier => supplier.SupplierID)
.Skip(startIndex)
.Take(maxRows).ToList();
}
}
So far so good. But then I add my DetailsView and try to wire it to my Gridview's selectedValue as the data source:
<asp:DetailsView ID="DetailsView1" runat="server" Height="50px" Width="125px" AutoGenerateRows="False" DataSourceID="SuppliersSingleItemDataSource">
<Fields>
<asp:BoundField DataField="SupplierID" HeaderText="SupplierID" SortExpression="SupplierID" />
<asp:BoundField DataField="CompanyName" HeaderText="CompanyName" SortExpression="CompanyName" />
</Fields>
</asp:DetailsView>
<asp:SqlDataSource ID="SuppliersSingleItemDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString2 %>"
SelectCommand="SELECT * FROM [Suppliers] WHERE ([SupplierID] = #SupplierID)">
<SelectParameters>
<asp:ControlParameter ControlID="gvSuppliers" DefaultValue="null" Name="SupplierID" PropertyName="SelectedValue" Type="Int32" />
</SelectParameters>
</asp:SqlDataSource>
As soon as I do this, I get the error you see in the opening of this question.
What I have tried:
Some Googling of this suggested I try limiting the columns displayed as BoundFields inside the DetailsView; that maybe there was bad data in the table. I have cut down the number of fields to a bare minimum, the SupplierID, which is an integer primary key and therefore can't be null or a non-integer value. I also kept the company name (a string).
Ensured I have an integer DataKeyName (SupplierID) specified in my gridview and it matches the datatype of the DetailViews' datasource (SupplierID, Int32).
The error message is so unhelpful and generic that I'm running out of ideas on how to solve this. Again, I am using this same technique (DetailsView picking up a Select in a Gridview) for other tables and not having this problem. I have painstakingly compared my technique on the pages that work against this one that doesn't work and cannot see a difference. It seems this should be working. Ideas, anyone?

Answer 1

I was able to solve this on my own. The culprit appears to be having a default value of null in the datasource for the the DetailsView. If I leave the default value out (hey,it was in the tutorial I was following!) the DetailsView won't try to display anything until it gets an actual integer from a click on the gridview. Thought I'd leave my question and answer here in case anybody else runs into this situation. Judging by Google, it is a quite common error.
<asp:SqlDataSource ID="SuppliersSingleItemDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString2 %>"
SelectCommand="SELECT * FROM [Suppliers] WHERE ([SupplierID] = #SupplierID)">
<SelectParameters>
<asp:ControlParameter ControlID="gvSuppliers" Name="SupplierID" PropertyName="SelectedValue" Type="Int32" />
</SelectParameters>
</asp:SqlDataSource>