Hi Jack,
Currently the width of the FileExplorer's context menus can be changed only on the client-side after the menus are shown. For example, you can do it the the context menus' onClientShown event handlers:
More detaile information regarding the client-side API of RadFileExplorer and the handled client events can be found here:
http://docs.telerik.com/devtools/aspnet-ajax/controls/fileexplorer/client-side-programming/overview
http://docs.telerik.com/devtools/aspnet-ajax/controls/menu/client-side-programming/events/onclientshown
http://docs.telerik.com/devtools/aspnet-ajax/controls/treeview/client-side-programming/events/onclientcontextmenushown
Regards,
Vessy
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