Gtk.Widget::grab-notify

function callback(widget, was_grabbed:Boolean, ):void;

The ::grab-notify signal is emitted when a widget becomes shadowed by a GTK+ grab (not a pointer or keyboard grab) on another widget, or when it becomes unshadowed due to a grab being removed.

A widget is shadowed by a Gtk.Widget.prototype.grab_add when the topmost grab widget in the grab stack of its window group is not its ancestor.