Thank you for writing.
The focus method is directly inherited by the System.Windows.Forms.Control class so you should be able to access it. Can you please confirm that you are using the RadMultiColumnComboBox
for WinForms? In case you keep having issues focusing the control please provide us with details about your actual scenario. A sample code snippet demonstrating your local setup would also help.
I hope this helps. Should you have further questions please do not hesitate to write back.