Hi Ranu,
Thanks for using Syncfusion Products.
If your intention is to get access and customize to the drop down portion of the ComboBoxAdv means please use comboBoxAdv1_SelectionChangeCommitted event,DropDownButton property in your application.
Please refer the attached sample.
http://websamples.syncfusion.com/samples/Tools.Windows/F63761/main.htmThe above sample which illustrates how to add a new comboBoxAdv item using comboBoxAdv1_SelectionChangeCommitted Event and use of DropDownButton property.
Please let me know if this helps.
Thanks and Regards,
Rashidha.