Signal for property changes

[Marcel Holtmann]

Hi Thiago,

> >So what about adding a signal to the properties introspection that
> >allows us to do this officially? Something like
> >
> >  org.freedesktop.DBus.Properties.Changed (STRING interface_name,
> >                                           STRING property_name,
> >                                           VARIANT value);
> >
> >Comments?
> 
> Yes: the signal not being emitted must not mean the property did not 
> change.

actually if we have that signal, it should mean exactly that. If you use
the Set method to change the property, the signal should be emitted. In
case the property value is changed via a system event or an external
tool or whatever, the signal should also be emitted. This is the only
way to keep property values in sync with UI applications without polling
all the time.

In case of BlueZ we do exactly this. For example if you use the command
line tool to change the friendly name (this goes directly via the kernel
interface) we still send out a signal that the name has changed.

I can see that in some cases this is not always possible. So what about
adding that signal, but also having an annotation for the property value
that indicates that such a signal is available for this property. This
would also allow backward compatibility with the current specification.

Regards

Marcel