The multi-column combobox is a special case of combobox control with RadGridView integrated in its drop-down. The control combines the functionality and features of RadDropDownList and RadGridView.
The image below represents the structure of the multi-column combobox.
The EditorControl property of the MultiColumnComboBoxElement gives you a reference to the RadGridView control. Using that reference you can obtain the RadGridView object and work as with normal RadGridView control. Refer to the RadGridView documentation for additional information on RadGridView.
The current version has some limitations that you should consider:
You cannot use the auto-complete mode of RadDropDownList
The RadGridView control hosted in the drop-down does not allow editing operations
The RadGridView control hosted in the drop-down does not support filtering, grouping and sorting operations.