RadDropDownList supports a number of server-side events that let you respond to events with complex actions that can't be performed in client-side code.
SelectedIndexChanged occurs when the SelectedIndex has just changed.
ItemSelected occurs when an item from the dropdownlist is selected.
ItemDataBound occurs for each item when it is being bound to a data value.
The SelectedIndexChanged and ItemSelected events do not fire unless you set the AutoPostBack property to True .