public class void install_action (string action_name, string? parameter_type, WidgetActionActivateFunc activate)
This should be called at class initialization time to specify actions to be added for all instances of this class.
Actions installed by this function are stateless. The only state they have is whether they are enabled or not (which can be changed with [ method@Gtk.Widget.action_set_enabled]).
a prefixed action name, such as "clipboard.paste"
the parameter type
callback to use when the action is activated