GtkWindow::activate_focus
activate_focus() is a method that will emit the activate signal from the child widget having focus at the point that the method is called. In GTK+, each widget has one signal which has activate signal status; the signal with this status has the ability to respond to events generated from the keyboard. If you do not have that widget-specific activate signal connected to the widget with focus, nothing will be fired.
The widget that is most likely to be used in this situation is probably GtkButton, which has "clicked" as its activate signal.
If this method is part of a callback called from another widget, that widget will have focus at the time that the callback is run and PHP will - understandably - crash. It needs to be called from an event signal in order to work.
See also: Signals and Events in the PHP-GTK userguide, activate_default() , set_focus() , "activate".
忘却曲線を使ってこの知識を確実に記憶に残す
