How to implement custom interfaces in derived TreeModelSort ?

[Gaëtan Frenoy <gaetan frenoy net>]

Hi,

What is the proper way to implement my own custom interface on top of 
Gtk3::TreeModelSort ?

Inspired by what is described in Glib::Object::Subclass[1], I tried the 
following:

---------------------------------------------------------------------------------------
package MyTreeModelSort;

use strict;
use Gtk3 -init;

use Glib::Object::Subclass
    'Gtk3::TreeModelSort',
    interfaces => [ 'Gtk3::TreeDragDest' ];

sub DRAG_DATA_RECEIVED {
    my ($dest_path, $selection_data) = @_;
    print("drag data received : $dest_path ; $selection_data ;\n");
    return 1;
}

sub ROW_DROP_POSSIBLE {
    my ($dest_path, $selection_data) = @_;
    print("row drop possible : $dest_path ; $selection_data ;\n");
    return 1;
}
---------------------------------------------------------------------------------------

But my custom methods are never called so there's something I do not do 
right ; for sure.  Any tip or suggestion will be warmly welcome.

Thanks for your help and collaboration :)

  Gaëtan


[1] https://metacpan.org/pod/Glib::Object::Subclass