gtk/box_since_3_12.go
func (a *Box) SetCenterWidget(child IWidget) {
	if child == nil {
		C.gtk_box_set_center_widget(a.native(), nil)
	} else {
		C.gtk_box_set_center_widget(a.native(), child.toWidget())
	}
}
func (a *Box) SetCenterWidget(child IWidget) {
	if child == nil {
		C.gtk_box_set_center_widget(a.native(), nil)
	} else {
		C.gtk_box_set_center_widget(a.native(), child.toWidget())
	}
}
//gtk_box_bar_set_center_widget(GtkBox *box,GtkWidget *center_widget)