Have you gone through the following online demo which shows how to implement LoadOnDemand Multi-column RadComboBox? If so could you please specify the difficulty that you have faced in achieving the desired scenario. Multi-column ComboBox
You can also refer the following demo link which shows how to integrate RadComboBox in RadGrid. Combo in Grid
I had gone through the demos already and have implemented the same kind of functionality in my project. The only issue is that I could not use the DataBind method of the RADComboBox (which is available in RADGrid EditItemTemplate) in ItemRequested event handler method of the RADComboBox.
It says some error message like Could not bind..Eval(), Xval()..etc..