Re: Glib - Object Properties

[Tristan Van Berkom <tvb gnome org>]

Shay Harding wrote:
> Hello,
>  
> I am new to Glib and have been working through constructing an object. I
> have an object working, but am having issues with the properties. I have
> the properties working (kind of), but some things don't make sense to me
> and was hoping someone could explain.
>  
> I have searched the web and mailing list archives, but can only find
> data circa 2004 or less and am not really sure if it still pertains
> today.
>  
> Currently, I can get/set properties no problem. The issues I am having
> pertain to how to trap errors during object construction for
> CONSTRUCT_ONLY properties. If I have a property with flags set to:
>  
> G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE
>  
> then I supposedly can only set the property while calling
> g_object_new(). This is only kind of true. If I attempt to set the
> property after g_object_new() is called, Glib simply emits a warning,
> but still allows the property to be set. Actually, this is only true if
> I call g_object_set_property() within my xxx_set_property() function.
> The problem is g_object_set_property() returns void so I have no way to
> catch errors (i.e. property set outside of a constructor).
>  
> How can CONSTRUCT_ONLY actually be enforced and not emit warnings to
> stdout/stderr? From what I can tell, I can't even write my own code to
> do this since I have no access to the static global 'pspec_pool' and the
> GParamSpec passed to my xxx_set_property() function after construct is
> NULL (incidentally it seems to always be NULL after the object is
> constructed even without CONSTRUCT_ONLY set in flags).
>  
> Thanks for any insight as to why this all works like this and any advice
> on enforcing policies.

Hi,
   "Construct only" properties were only enforced in GTK+ >= 2.4,
If you are using the latest GTK+, then your xxx_set_property method
"shouldn't get envoked" when setting properties on your object.

You should never call g_object_set_property () from inside your
xxx_set_property method, this will result in endless recursion,
the set_property method is a private method used only to actualy
persist the transported GValue on your actual instance.

Cheers,
                           -Tristan