The DevExpress ASP.NET Drop-down Edit (ASPxDropDownEdit) represents an editor containing an edit box to display the editor value (defined via the Text property) and a specific button that opens a drop-down window whose content can be templated (using the DropDownWindowTemplate property). The ASPxDropDownEdit allows you to define its value based on the value of another control (or the values of other controls) integrated into the editor's DropDownWindowTemplate.
In this demo, a DevExpress ASP.NET Tree List (ASPxTreeList) control is placed in the dropdown window template of ASPxDropDownEdit. To change the editor value, select a Tree List node and click the Select button. A specific client API exposed by the ASPxDropDownEdit is used in this demo to assign text and a value to the editor (the SetText and SetKeyValue methods), and hide the editor's dropdown window (the HideDropDown method).