Accessing GtkWidget class methods

[danirod]

Hello there. I am looking for suggestions in regards to using the class methods for the GtkWidget class. In gtk-rs, these methods are part of the WidgetClassExt, but I can't get my head around how to get access to those methods. In my case, the goal is to have access to the add_shortcut method (docs.rs, GTK) so that I can install shortcuts into every instance of a specific widget.

I am writing a GTK 4 application and while GNU/Linux is the preferred platform, I am doing my best to make sure that the application looks and works right in Windows and macOS too. In GTK 4, the <Primary> keyboard modifier is bound to the Control key even on macOS, where most users would expect the <Meta> modifier. This means that, by default, the shortcuts for built-in actions like copy and paste from a text field are Ctrl-C and Ctrl-V rather than Cmd-C and Cmd-V, unless the application changes them.

In this specific example, Gaphor is using the following Python code to change the shortcuts of the selection.select-all action part of the Gtk.TextView widget class, so that every instance of Gtk.TextView uses the new shortcut (the code is actually more complex becuase they are using a function to encapsulate building the shortcut):

Gtk.TextView.add_shortcut(
    new_shortcut_with_args(
        "<Meta>a", "select-all",
        GLib.Variant.new_boolean(True)
    )
)

One of the benefits of the GObject introspection is that it is very easy to translate code from between languages. However, even if I suspect it cannot be that difficult, I can't call the add_shortcut function because I don't know how to get a code path to that method.

If this was a custom widget, I could just use the class_init function when implementing ObjectSubclass for my widget, because I have a Class parameter, but when I try to apply it to the GtkText and GtkTextView widgets like the code I show above, I am not having any luck.

For C and Python, the function calls are more obvious (gtk_widget_class_add_shortcut and Gtk.TextView.add_shortcut), but in Rust it is being a challenge. I don't know if I am supposed to just use gtk::TextView::add_shortcut() and make sure that I am using the WidgetClassExt trait in my file (on a first try, doesn't seem to work), or if I have to use a function to get the class first. I've played with the following, but it doesn't compile.

let trigger = gtk::ShortcutTrigger::parse_string("<Meta>c").unwrap();
let shortcut = gtk::Shortcut::new(Some(trigger), Some(gtk::NamedAction::new("clipboard.copy")));

let text_type = gtk::TextView::static_type();
let text_class = glib::object::Class::from_type(text_type).unwrap();
text_class.add_shortcut(&trigger);

I've checked the source code for other programs written in gtk-rs to see if I can learn something from them, but it seems that none of them has had the need to use this function so far.

Any advice? Thanks in advance.

[bilelmoussaoui]

The problem comes from the trait constraints imposed at

unsafe impl<T: ClassStruct> WidgetClassExt for T where T::Type: WidgetImpl {}

it should be something like

unsafe impl<T: IsA<Widget> + glib::object::IsClass> WidgetClassExt for glib::object::Class<T> {}

instead

[bilelmoussaoui]

Could you convert the discussion to an issue please?

[danirod]

Sure!

Created issue as #1793