Handling Focus

GtkEv wants to receive key press events so it can report information about them. As discussed in the section called Focus in the chapter called GTK+ Basics and the section called Keyboard Focus in the chapter called GDK Basics, only toplevel windows receive key events from GDK. GtkWindow keeps track of a current focus widget and forwards key events to it.

If a widget wants to receive key events, it must:

• Set its GTK_CAN_FOCUS flag, so GTK+ will consider it as a possible focus widget.

• Respond to "focus_in" and "focus_out" signals by drawing and erasing a visual indication that it has the focus.

GtkEv set the GTK_CAN_FOCUS flag in gtk_ev_init(); it implements focus in and focus out methods as follows:

static gint 
gtk_ev_focus_in       (GtkWidget        *widget,
                       GdkEventFocus    *event)
{
  g_return_val_if_fail(widget != NULL, FALSE);
  g_return_val_if_fail(GTK_IS_EV(widget), FALSE);

  GTK_WIDGET_SET_FLAGS (widget, GTK_HAS_FOCUS);
  gtk_widget_draw_focus (widget);

  return FALSE;
}

static gint 
gtk_ev_focus_out      (GtkWidget        *widget,
                       GdkEventFocus    *event)
{
  g_return_val_if_fail(widget != NULL, FALSE);
  g_return_val_if_fail(GTK_IS_EV(widget), FALSE);

  GTK_WIDGET_UNSET_FLAGS (widget, GTK_HAS_FOCUS);
  gtk_widget_draw_focus (widget);

  return FALSE;
}
      

These implementations are the minimal ones; all focusable widgets must set or unset the GTK_HAS_FOCUS flag when they gain or lose the focus, and they must emit the "draw_focus" signal.

GtkEv has a lazy implementation of the "draw_focus" signal; it just calls the same gtk_ev_paint() used to respond to expose events and redraw requests. Recall that gtk_ev_paint() checks whether the GtkEv has the focus and draws a focus frame if so. Here is the code:

static void 
gtk_ev_draw_focus     (GtkWidget        *widget)
{
  GdkRectangle rect;
  GtkEv* ev;

  g_return_if_fail(widget != NULL);
  g_return_if_fail(GTK_IS_EV(widget));

  ev = GTK_EV(widget);

  rect.x = 0;
  rect.y = 0;
  rect.width = widget->allocation.width;
  rect.height = widget->allocation.height;

  if (GTK_WIDGET_DRAWABLE (ev))
    gtk_ev_paint(ev, &rect);
}
      

Notice that widget implementations are responsible for emitting the "draw_focus" signal themselves; GTK+ does not emit it as the focus moves. Contrast this with the "draw_default" signal, which GTK+ automatically emits whenever a widget gains or loses the default. GtkEv cannot be the default widget, so it does not implement this signal.