gtk-sharp Gtk# is thread aware, but not thread safe; See the Gtk# Thread Programming for details. System.Delegate System.Void Event sender. Event arguments. Event handler. The event utilizes this delegate: Event data is passed via the parameter. To attach a to an event, add the FocusInEventHandler instance to the event. The methods referenced by the FocusInEventHandler instance are invoked whenever the event is raised, until the FocusInEventHandler is removed from the event.