Thank you for writing.
Attached you can find the requested sample project with the desired functionality. However, I would like to suggest to take a look at our GridViewMultiComboBoxColumn
, which consists of a RadGridView inside of a popup. As you know, RadGridView provide filtering, grouping and other data operations and it will not need custom actions to build it.
I hope that you find this information helpful. Should you have any other questions, do not hesitate to contact us.
the Telerik team
Q2’11 SP1 of RadControls for WinForms is available for download (see what's new); also available is the Q3'11 Roadmap for Telerik Windows Forms controls.