The ASP.NET page framework calls the DropDownList.RaisePostDataChangedEvent method on a System.Web.UI.WebControls.DropDownList control when the DropDownList.LoadPostData(string, System.Collections.Specialized.NameValueCollection) method indicates that the state of the list items has changed in the System.Web.UI.WebControls.DropDownList control. The DropDownList.RaisePostDataChangedEvent method calls the ListControl.OnSelectedIndexChanged(EventArgs) method to raise the ListControl.SelectedIndexChanged event. Control developers can override the ListControl.OnSelectedIndexChanged(EventArgs) method to perform custom processing when the user selects items in the control.