Hi Reinout,

You can see how to sort the items in the grid in this KB article: Sorting RadFileExplorer items by name.
You can find a solution for your request in this forum thread: How to add a time column to DialogOpener window?

Please, note that the grid items are initially sorted on the server, when the dialog is loaded. We sort them on the client only the items on page 1 of the grid paging, but not all items. To achieve your scenario you should disable the paging and populate all files when the dialog is started. To do this open the FileBrowser.ascx file, locate the RadFileExplorer control and set AllowPaging to false, e.g.

<telerik:RadFileExplorer ID="RadFileExplorer1" Height="450px" Width="400px" TreePaneWidth="150px"
 runat="Server" EnableOpenFile="false" AllowPaging="false" />

Another approach is to register the external dialog files of RadEditor,

Regards,
Rumen
Progress Telerik