GtkWindow::activate_focus
int activate_focus(void); 
    
     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".