TActiveDropDownList
API Manual
TActiveDropDownList is the active counterpart to the original TDropDownList control.
The AutoPostBack property is set to true by default.
Thus, when the drop down list selection is changed the OnCallback event is
raised after OnSelectedIndexChanged event.
With ActiveControl.EnableUpdate
set to true (default is true), changes to the selection, after OnLoad event has
been raised, will be updated on the client side.
List items can be changed dynamically during a callback request.
Please refer to the original documentation of TDropDownList for usage.