z144.html

GTK+_ Gnome Application Development

                                GdkModifierType accel_mods);

  /* Explicit focus */
  void (* grab_focus)          (GtkWidget      *widget);
  
  /* Events */
  gint (* event)                   (GtkWidget          *widget,
                                    GdkEvent           *event);
  gint (* button_press_event)      (GtkWidget          *widget,
                                    GdkEventButton     *event);
  gint (* button_release_event)    (GtkWidget          *widget,
                                    GdkEventButton     *event);
  gint (* motion_notify_event)     (GtkWidget          *widget,
                                    GdkEventMotion     *event);
  gint (* delete_event)            (GtkWidget          *widget,
                                    GdkEventAny        *event);
  gint (* destroy_event)           (GtkWidget          *widget,
                                    GdkEventAny        *event);
  gint (* expose_event)            (GtkWidget          *widget,
                                    GdkEventExpose     *event);
  gint (* key_press_event)         (GtkWidget          *widget,
                                    GdkEventKey        *event);
  gint (* key_release_event)       (GtkWidget          *widget,
                                    GdkEventKey        *event);
  gint (* enter_notify_event)      (GtkWidget          *widget,
                                    GdkEventCrossing   *event);
  gint (* leave_notify_event)      (GtkWidget          *widget,
                                    GdkEventCrossing   *event);
  gint (* configure_event)         (GtkWidget          *widget,
                                    GdkEventConfigure  *event);
  gint (* focus_in_event)          (GtkWidget          *widget,
                                    GdkEventFocus      *event);
  gint (* focus_out_event)         (GtkWidget          *widget,
                                    GdkEventFocus      *event);
  gint (* map_event)               (GtkWidget          *widget,
                                    GdkEventAny        *event);
  gint (* unmap_event)             (GtkWidget          *widget,
                                    GdkEventAny        *event);
  gint (* property_notify_event)   (GtkWidget          *widget,
                                    GdkEventProperty   *event);
  gint (* selection_clear_event)   (GtkWidget          *widget,
                                    GdkEventSelection  *event);
  gint (* selection_request_event) (GtkWidget          *widget,
                                    GdkEventSelection  *event);
  gint (* selection_notify_event)  (GtkWidget          *widget,
                                    GdkEventSelection  *event);
  gint (* proximity_in_event)      (GtkWidget          *widget,
                                    GdkEventProximity  *event);
  gint (* proximity_out_event)     (GtkWidget          *widget,
                                    GdkEventProximity  *event);
  gint (* visibility_notify_event)  (GtkWidget         *widget,
                                     GdkEventVisibility *event);
  gint (* client_event)            (GtkWidget          *widget,
                                    GdkEventClient     *event);
  gint (* no_expose_event)         (GtkWidget          *widget,
                                    GdkEventAny        *event);

  /* Selection */
  void (* selection_get)           (GtkWidget          *widget,
                                    GtkSelectionData   *selection_data,
                                    guint               info,
                                    guint               time);
  void (* selection_received)      (GtkWidget          *widget,
                                    GtkSelectionData   *selection_data,
                                    guint               time);

  /* Source side drag signals */
  void (* drag_begin)              (GtkWidget          *widget,
                                    GdkDragContext     *context);
  void (* drag_end)                (GtkWidget          *widget,
                                    GdkDragContext     *context);
  void (* drag_data_get)           (GtkWidget          *widget,
                                    GdkDragContext     *context,
                                    GtkSelectionData   *selection_data,
                                    guint               info,
                                    guint               time);
  void (* drag_data_delete)        (GtkWidget          *widget,
                                    GdkDragContext     *context);

  /* Target side drag signals */
  void (* drag_leave)              (GtkWidget          *widget,
                                    GdkDragContext     *context,
                                    guint               time);
  gboolean (* drag_motion)         (GtkWidget          *widget,
                                    GdkDragContext     *context,
                                    gint                x,
                                    gint                y,
                                    guint               time);
  gboolean (* drag_drop)           (GtkWidget          *widget,
                                    GdkDragContext     *context,
                                    gint                x,
                                    gint                y,
                                    guint               time);
  void (* drag_data_received)      (GtkWidget          *widget,
                                    GdkDragContext     *context,
                                    gint                x,
                                    gint                y,
                                    GtkSelectionData   *selection_data,
                                    guint               info,
                                    guint               time);
  
  /* Action signals */
  void (* debug_msg)               (GtkWidget          *widget,
                                    const gchar        *string);

  /* Padding for future expansion */
  GtkFunction pad1;
  GtkFunction pad2;
  GtkFunction pad3;
  GtkFunction pad4;
};
      
</pre>
            </td>
          </tr>
        </table>
        <p>
          Most of the functions in <span class="STRUCTNAME">
          GtkWidgetClass</span> are registered as default handlers
          for signals. The exceptions are <span class="STRUCTNAME">
          show_all</span> and <span class="STRUCTNAME">
          hide_all</span>, which are class functions only. Of
          course, <span class="STRUCTNAME">GtkWidgetClass</span>
          inherits the five class functions and single signal
          (<span class="SYMBOL">"destroy"</span>) from <span class= 
          "STRUCTNAME">GtkObjectClass</span>. This chapter will
          describe the important methods in more detail; also, <a
          href="sec-gdkevent.html">the section called <i>Events</i>
          in the chapter called <i>GDK Basics</i></a> is important
          for understanding the event methods. <a href= 
          "sec-widgetindetail.html">the section called <i><tt
          class="CLASSNAME">GtkWidget</tt> In Detail</i></a>
          describes the default implementation of each method in
          some detail.
        </p>
        <div class="SECT3">
          <h3 class="SECT3">
            <a name="SEC-OVERRIDESIGNALS">Overridable Signals</a>
          </h3>
          <p>
            You may notice that <span class="STRUCTNAME">
            GtkWidgetClass</span> contains two signal identifiers
            in addition to function pointers. These are 0 by
            default; otherwise, they indicate the signal to emit to
            "activate" the widget, or to set its scroll
            adjustments.
          </p>
          <p>
            The <span class="STRUCTNAME">activate_signal</span> is
            emitted when the user presses the space bar or Enter
            key while the widget is focused; for buttons, it will
            be the <span class="SYMBOL">"clicked"</span> signal,
            for menu items, the <span class="SYMBOL">
            "activate"</span> signal.
          </p>
          <p>
            The <span class="STRUCTNAME">
            set_scroll_adjustments_signal</span> is used by <tt
            class="CLASSNAME">GtkScrolledWindow</tt> to set the
            scroll adjustments used by the widget. <tt class= 
            "CLASSNAME">GtkLayout</tt>, <tt class="CLASSNAME">
            GtkCList</tt>, and others have a signal to set the
            scroll adjustments.
          </p>
          <p>
            These two hacks are necessary because GTK+ 1.2 does not
            support interfaces or multiple inheritance. (A future
            version of GTK+ may support interfaces similar in
            spirit to Java's interfaces.) Ideally, there would be
            "GtkActivatable" and "GtkScrollable" base classes or
            interfaces, and all widgets supporting these actions
            would derive from them. Including the two signal IDs in
            <span class="STRUCTNAME">GtkWidgetClass</span> is a
            short-term workaround.
          </p>
        </div>
      </div>
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          <td colspan="2" align="left">
            <font color="#000000" size="2"><b>Writing a <tt class= 
            "CLASSNAME">GtkWidget</tt></b></font>
          </td>
          <td colspan="2" align="right">
            <font color="#000000" size="2"><b>An Example: The <tt
            class="CLASSNAME">GtkEv</tt> Widget</b></font>
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