WidgetActionActivateFunc   
    typealias WidgetActionActivateFunc = (widget: Widget, actionName: String, <Error class: unknown class>?) -> Unit(source)
The type of the callback functions used for activating actions installed with gtk_widget_class_install_action().
The @parameter must match the @parameter_type of the action.
- param - widgetthe widget to which the action belongs
- param - actionNamethe action name
- param - parameterparameter for activation