Hi Ravi,
ComboBoxBase has inherited the characteristics of AutoComplete and List derived controls. We can achieve this by implementing the list control with the ComboBoxBase control. I have attached a sample for your reference. Please take a look at this and let me know if you have any quires regarding this.
Thanks for choosing Syncfusion products.
Regards,
Velmurugan E.
Forum_ComboBoxBaseControl.zip