Load on Demand Sample Using ItemPopulate event Using CallbackDataBind event Description The C1ComboBox control supports filling the dropdown list dynamically as the user scrolls. You can fill the list by using two different methods: OnItemPopulate or OnCallbackDataBind. If the C1ComboBox is not bound to a datasource, you can populate the items using the corresponding properties: OnItemPopulate : EnableCallBackMode: true CallbackDataPopulate:ItemPopulate OnItemPopulate The OnItemPopulate event will be raised when C1ComboBox requests data from client side.   CallbackDataBind: EnableCallBackMode: true OnCallbackdatabind The OnCallbackDatabind event will be raised when C1ComboBox requests data from the data source. Documentation