ListBox with Entity Framework

I am data binding a I开发者_如何学GoQueryable collection of Suppliers to a listbox as follows in my page load event...

        SupplierRepository sr = SupplierRepository.GetInstance();
        lbSuppliers.DataSource = sr.FindAll();
        lbSuppliers.DataTextField = "SupplierName";
        lbSuppliers.DataValueField = "SupplierID";
        lbSuppliers.DataBind();

But for some reason when I try to get the selectedvalue from the list box as follows it's returning null, even though I can see the values in the html source view at runtime.

lbSuppliers.SelectedValue.ToString();

Seems a very basic problem, but I am stuck. Is this because I am using a EF collection for the data source?

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Are you binding every PageLoad? If you are, then the SelectedItem will disappear.

Try wrapping the DataBinding code in an If (!IsPostBack) block.