Cocoa finder menu item for folders only - objective-c

Question

I am trying to create a Finder context menu item using a service (as described here: Writing a Snow Leopard Service for Finder.app )
However, I wish to add a context menu entry for folders only.
Whenever I put the following code in my .plist file:
<key>NSServices</key>
<array>
<dict>
<key>NSMenuItem</key>
<dict>
<key>default</key>
<string>Service Handling Demo</string>
</dict>
<key>NSMessage</key>
<string>handleServices</string> <!-- This specifies the selector -->
<key>NSPortName</key>
<string>Tmp</string> <!-- This is the name of the app -->
<key>NSSendTypes</key>
<array>
<string>NSFilenamesPboardType</string>
</array>
</dict>
</array>
Everything works fine, I can select my service in the Services tab (keyborad shourtcuts) and run it.
However, if I try to use the service for folders:
<key>NSServices</key>
<array>
<dict>
<key>NSMenuItem</key>
<dict>
<key>default</key>
<string>Service Handling Demo</string>
</dict>
<key>NSMessage</key>
<string>handleServices</string> <!-- This specifies the selector -->
<key>NSPortName</key>
<string>Tmp</string> <!-- This is the name of the app -->
<key>NSSendFileTypes</key>
<array>
<string>public.directory</string>
</array>
<key>NSSendTypes</key>
<array>
<string>NSStringPboardType</string>
</array>
</dict>
</array>
The service does not appear in the keyboard shortcuts' menu and of course is not visible in finder...
What am I missing?

Answer 1

Add the following code to the .plist:
<key>NSServices</key>
<array>
<dict>
<key>NSMenuItem</key>
<dict>
<key>default</key>
<string>Folder Handling Demo</string>
</dict>
<key>NSMessage</key>
<string>handleServices</string> <!-- This specifies the selector -->
<key>NSPortName</key>
<string>Tmp</string> <!-- This is the name of the app -->
<!-- Here we're limiting where the service will appear. -->
<key>NSRequiredContext</key>
<dict>
<key>NSTextContent</key>
<string>FilePath</string>
</dict>
<!-- This service is only really useful from the Finder. So
we want the finder only to send us the URI "public.directory"
which *will* include packages (on the off-chance you want to
see the full package directory name) -->
<key>NSSendFileTypes</key>
<array>
<!-- Check out "System-Declared Uniform Type Identifiers"
in the Apple documentation for the various UTI types.
In this example, all we want is a directory, which is
a super-type to other types (e.g. public.folder) -->
<string>public.folder</string>
</array>
</dict>
And the service will appear under "Files and Folders" group in the services list (keyboard shortcuts tab).