Default values for properties

[Martin Baulig <martin home-of-linux org>]

Hi guys,

I have some little problem with the default values of the properties.

In GnomeSelector, I have some G_PARAM_CONSTRUCT_ONLY properties:

    /* Construction properties */
    PROP_ENTRY_WIDGET,
    PROP_SELECTOR_WIDGET,
    PROP_BROWSE_DIALOG,
    PROP_WANT_DEFAULT_BEHAVIOUR,
    PROP_USE_DEFAULT_ENTRY_WIDGET,
    PROP_USE_DEFAULT_SELECTOR_WIDGET,
    PROP_USE_DEFAULT_BROWSE_DIALOG,
    PROP_WANT_BROWSE_BUTTON,
    PROP_WANT_CLEAR_BUTTON,
    PROP_WANT_DEFAULT_BUTTON,
    PROP_AUTO_SAVE_HISTORY,
    PROP_AUTO_SAVE_ALL,

In the subclasses, for instance GnomeEntry or GnomeIconSelector, I want
to provide some default values for these properties to specify the default
"look&feel" of the widget.

For instance, I want to be able to use

        entry = g_object_new (gnome_entry_get_type(),
                              "auto_save_history", TRUE,
                              NULL);

to create a GnomeEntry which automatically saves history.

I also want to be able to override some of these properties, for instance

        iconsel = g_object_new (gnome_icon_selector_new(),
                                "want_default_button", FALSE,
                                NULL);

to get a widget which looks&feels like a GnomeIconSelector, but doesn't
have a "Default" button.

Now, my problem is that I can specify a default value for these properties
in the class where they're defined (GnomeSelector), but I cannot alter the
default value in a derived class (which is a good thing, IMO).

While doing some debugging, I realized that on object creation the
`set_property()' method is called for all properties and not only for the
ones that were given to g_object_new().

This means that my `set_property()' handler can't figure out whether the
user explicitly set a property or whether it's just the default value of it.

What do you think about adding a G_PARAM_NODEFAULT flag to request that a
property won't get its default value if it isn't explicitly set ?

-- 
Martin Baulig
martin gnome org (private)
baulig suse de (work)