add combo box field to table cell

I'm trying to add a comboboxfield to a table cell, but receiving nullexception error. I don't think I'm instantiating the comboboxfield correctly, but can't seem to find any examples to apply to what I'm doing.

I've attached the source code showing how I'm creating the table, rows and cells. I create the header row declaratively, then loop a data returned from sql datareader to build the data rows.

Thank you.