Re: Setting custom Glib::Property values in Gtk::Builder .ui XML

[Kjell Ahlstedt <kjellahlstedt gmail com>]

On 6/13/19 2:41 PM, Daniel Boles via gtkmm-list wrote:
> > for posterity, it looks like someone else has had the same questions 
> but didn't get much further:
>
> That user was also using wrap_register() to have code called when 
> glibmm wraps the C instances. I know next to nothing about that - but 
> I wonder if it's at all possible that it could be used with 
> builder->get_objects() in order to ensure everything gets wrapped, and 
> custom code in the registered wrap_new() function to apply the derived 
> properties? However, it seems that user didn't get that to work, if I 
> understood correctly.
I've made a similar test. It failed.

I started with gtkmm-documentation/examples/book/builder/derived and 
replaced the GtkButton with
  class MyButton : public Gtk::Button
with a few custom properties. I used Glib::Property for those 
properties. In the .ui file:
  <object class="gtkmm__CustomObject_MyButton" id="quit_button">

MyButton has
  MyButton(GtkButton* castitem);
  static Glib::ObjectBase* wrap_new(GObject* object);
and I call
Glib::wrap_register(g_type_from_name("gtkmm__CustomObject_MyButton"), 
&MyButton::wrap_new);
after having created a dummy MyButton instance to have the class init 
function called.

The only problem is that the custom property values, specified in the 
.ui file, are not stored anywhere. Glib::Property stores custom property 
values in the C++ code, but GtkBuilder creates a C instance of MyButton 
and tries to store the property values before Gtk::Builder::get_widget() 
has created the C++ wrapper. Glib::custom_set_property_callback() in 
glibmm/property.cc discards the values.

Conclusion: It's not possible to combine Glib::Property with Gtk::Builder.