[Vala] How to use GLib.Signal.connect?

[Pete Fotheringham <pete fotheringham codethink co uk>]

I am working with Vala and GtkOSXApplication on Mac OS. I am using Vala 
0.12 because I need to use dbus-glib and, as I understand it, this is 
not supported by versions of Vala beyond 0.12.1

I need to connect to a Mac Specific mac-specific NSApplicationOpenFile 
signal, which is generated by GtkOSXApplication.

If I use the line
> osxApp.NSApplicationOpenFile.connect(..)

the name of the signal is changed in the generated c code to 
"ns_application_open_file", and when the code is run the following error 
is generated
> GLib-GObject-WARNING **: gsignal.c:2206: signal `ns-application-open-file' is invalid for instance 
> `0x1401d020'

So I try to connect using
> Signal.connect(osxApp, "NSApplicationOpenFile", this.open_file_callback, this);
and the Vala compiler generates an error
> error: Cannot create delegate without target for instance method or closure
> Signal.connect(osxApp, "NSApplicationOpenFile", this.open_file_callback, this);
>                                                 ^^^^^^^^^^^^^^^^^^^^^^^
Can anyone give me an example of how to use Signal.connect() or suggest 
an alternative method?

More code details at http://fpaste.org/NxLO/

Thanks


--
Pete Fotheringham
Codethink Ltd
http://codethink.co.uk