CascadingDropDown Description

CascadingDropDown is an ASP.NET AJAX extender that can be attached to an ASP.NET DropDownList control to get automatic population of a set of DropDownList controls. Each time the selection of one the DropDownList controls changes, the CascadingDropDown makes a call to a specified web service to retrieve the list of values for the next DropDownList in the set.

CascadingDropDown enables a common scenario in which the contents of one list depends on the selection of another list and does so without having to embed the entire data set in the page or transfer it to the client at all. All the logic about the contents of the set of DropDownList controls lives on the server in a web service. This web service can use any suitable method for storing and looking up the relevant data. The sample web service used here reads the data set from a simple hierarchical XML data file. The sample data file shows that the DropDownList items can have distinct names and value (values are optional in the sample). There is also a walkthrough showing how to use a CascadingDropDown with a database.