This demo demonstrates how you can use RadTreeList to display the contents of a directory. This is achieved by populating an XML file with items describing a folder's structure and content. Then RadTreeList is bound to an XmlDataSource populated by this file.
Expand/Collapse on double click is done by wiring the OnItemDblClick client event and checking whether the current item represents a file or folder in order to determine whether an ExpandCollapse command should be fired.
The single click functionality is achieved by accessing the fields of the currently selected item (single selection) on the client and displaying their values in an info panel.