How to enable Selection for a GridView that assigns the DataSource in the code behind class?

Hi, I noticed that when I create a GridView that I am given the option to "Enable Selection" as long as I choose a DataSource in the GUI. However, I am binding the DataSource in the code behind class.

I added SelectMethod="GetCustomers" to my GridView control and an empty GetCustomers() method to my code behind class but I don't see a "Select" link appear in my GridView.

How can I enable "Selection" for my GridView if the DataSource is being bound in the code behind?

Not sure if this is relevant but my data is coming from my NorthwindDAL.GetCustomers() method which is returning a List of type <Customers>.