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20. 写出属於您自己的物件

20.1 概说

虽然GTK的物件基本上是够用了, 但有时您还是需要产生自己所需要的物件型态. 如果已经有一个既存的物件很接近您的需求, 那麽您可以把程式改个几行就可以达到您的需求了. 但在您决定要写一个新的物件之前, 先确认是否有人已经写过了. 这会避免重复浪费资源, 并保持物件数量达到最少, 这会使程式及介面比较统一一点. 另一方面, 一旦您写好您的物件, 要向全世界公告, 这样其它人才会受益. 最好的公告地点大概就是gtk-list了.

20.2 物件的解析

为了要产生一个新的物件, 了解GTK的运作是很重要的. 这里只简单的说一下. 详细请参照reference documentation.

GTK物件是以流行的物件导件的观念来设计的. 不过, 依然是以C来写的. 比起用C++来说, 这可以大大改善可移植性及稳定性. 但同时, 这也意味著widget writer需要小心许多实作上的问题. 所有同一类别的物件的一般资讯 (例如所有的按钮物件)是放在 class structure. 只有一份这样的结构. 在这份结构中储存类别信号的资讯. 要支撑这样的继承, 第一栏的资料结构必须是其父类别的资料结构. 例如GtkButton的类别宣告看起来像这样:

struct _GtkButtonClass
{
  GtkContainerClass parent_class;

  void (* pressed)  (GtkButton *button);
  void (* released) (GtkButton *button);
  void (* clicked)  (GtkButton *button);
  void (* enter)    (GtkButton *button);
  void (* leave)    (GtkButton *button);
};

当一个按钮被看成是个container时(例如, 当它被缩放时), 其类别结构可被传到GtkContainerClass, 而其相关的栏位被用来处理信号.

对每个物件结构来说, 都有一些状况上的不同. 该结构都有一些资讯是不太一样的. 我们称此结构为object structure. 如按钮一类, 看起来像这样:

struct _GtkButton
{
  GtkContainer container;

  GtkWidget *child;

  guint in_button : 1;
  guint button_down : 1;
};

可以看到, 第一栏是其父类别的物件资料结构, 因此该结构可以传到其父类别的物件结构来处理.

20.3 产生一个组合物件

标头档

每个物件类别都有一个标头档来宣告其物件, 类别结构及其函数. 有些特性是值得指出的. 要避免重复宣告, 我们将整个标头档包成:

#ifndef __TICTACTOE_H__
#define __TICTACTOE_H__
.
.
.
#endif /* __TICTACTOE_H__ */

而且加入让C++程式不会抓狂的定义码:

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */
.
.
.
#ifdef __cplusplus
}
#endif /* __cplusplus */

除了函数及结构外, 我们宣告了三个标准巨集在标头档中 TICTACTOE(obj), TICTACTOE_CLASS(klass), 及IS_TICTACTOE(obj), 当我们传入一个指标到物件或类别结构中, 它会检查是否是我们的tictactoe物件.

这里是完整的标头档:


#ifndef __TICTACTOE_H__
#define __TICTACTOE_H__

#include <gdk/gdk.h>
#include <gtk/gtkvbox.h>

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */

#define TICTACTOE(obj)          GTK_CHECK_CAST (obj, tictactoe_get_type (), Tictactoe)
#define TICTACTOE_CLASS(klass)  GTK_CHECK_CLASS_CAST (klass, tictactoe_get_type (), TictactoeClass)
#define IS_TICTACTOE(obj)       GTK_CHECK_TYPE (obj, tictactoe_get_type ())


typedef struct _Tictactoe       Tictactoe;
typedef struct _TictactoeClass  TictactoeClass;

struct _Tictactoe
{
  GtkVBox vbox;
  
  GtkWidget *buttons[3][3];
};

struct _TictactoeClass
{
  GtkVBoxClass parent_class;

  void (* tictactoe) (Tictactoe *ttt);
};

guint          tictactoe_get_type        (void);
GtkWidget*     tictactoe_new             (void);
void           tictactoe_clear           (Tictactoe *ttt);

#ifdef __cplusplus
}
#endif /* __cplusplus */

#endif /* __TICTACTOE_H__ */

_get_type()函数.

我们现在来继续做我们的物件. 对每个物件来说, 都有一个重要的核心函数 WIDGETNAME_get_type(). 这个函数, 当第一次被呼叫的时候, 会告诉GTK有关该物件类别, 并取得一个ID来辨视其物件类别. 在其後的呼叫中, 它会返回该ID.

guint
tictactoe_get_type ()
{
  static guint ttt_type = 0;

  if (!ttt_type)
    {
      GtkTypeInfo ttt_info =
      {
        "Tictactoe",
        sizeof (Tictactoe),
        sizeof (TictactoeClass),
        (GtkClassInitFunc) tictactoe_class_init,
        (GtkObjectInitFunc) tictactoe_init,
        (GtkArgFunc) NULL,
      };

      ttt_type = gtk_type_unique (gtk_vbox_get_type (), &ttt_info);
    }

  return ttt_type;
}

GtkTypeInfo结构有以下定义:

struct _GtkTypeInfo
{
  gchar *type_name;
  guint object_size;
  guint class_size;
  GtkClassInitFunc class_init_func;
  GtkObjectInitFunc object_init_func;
  GtkArgFunc arg_func;
};

这资料结构自我解释的很好. 在此, 我们将会忽略掉arg_func这一栏: 它很重要, 可以允许用来给设定解译式语言来设定, 但大部份相关工作都还没有完成. 一旦GTK被正确的填入该资料结构, 它会知道如何产生某一个特别的物件类别.

The _class_init() function

WIDGETNAME_class_init()函数启始设定该物件类别的资料, 并设定给该类别信号.


enum {
  TICTACTOE_SIGNAL,
  LAST_SIGNAL
};

static gint tictactoe_signals[LAST_SIGNAL] = { 0 };

static void
tictactoe_class_init (TictactoeClass *class)
{
  GtkObjectClass *object_class;

  object_class = (GtkObjectClass*) class;
  
  tictactoe_signals[TICTACTOE_SIGNAL] = gtk_signal_new ("tictactoe",
                                         GTK_RUN_FIRST,
                                         object_class->type,
                                         GTK_SIGNAL_OFFSET (TictactoeClass, tictactoe),
                                         gtk_signal_default_marshaller, GTK_ARG_NONE, 0);


  gtk_object_class_add_signals (object_class, tictactoe_signals, LAST_SIGNAL);

  class->tictactoe = NULL;
}

该函数只有一个信号, ``tictactoe''信号. 并非所有组合式物件都需要信号, 所以如果这是您第一次读这里, 您可以跳到下一个, 因为这里有点复杂.

gint   gtk_signal_new                     (gchar               *name,
                                           GtkSignalRunType     run_type,
                                           gint                 object_type,
                                           gint                 function_offset,
                                           GtkSignalMarshaller  marshaller,
                                           GtkArgType           return_val,
                                           gint                 nparams,
                                           ...);

产生新讯号, 参数包含:

当指定型态时, 可用GtkArgType:

typedef enum
{
  GTK_ARG_INVALID,
  GTK_ARG_NONE,
  GTK_ARG_CHAR,
  GTK_ARG_SHORT,
  GTK_ARG_INT,
  GTK_ARG_LONG,
  GTK_ARG_POINTER,
  GTK_ARG_OBJECT,
  GTK_ARG_FUNCTION,
  GTK_ARG_SIGNAL
} GtkArgType;

The _init() function.


static void
tictactoe_init (Tictactoe *ttt)
{
  GtkWidget *table;
  gint i,j;
  
  table = gtk_table_new (3, 3, TRUE);
  gtk_container_add (GTK_CONTAINER(ttt), table);
  gtk_widget_show (table);

  for (i=0;i<3; i++)
    for (j=0;j<3; j++)
      {
        ttt->buttons[i][j] = gtk_toggle_button_new ();
        gtk_table_attach_defaults (GTK_TABLE(table), ttt->buttons[i][j], 
                                   i, i+1, j, j+1);
        gtk_signal_connect (GTK_OBJECT (ttt->buttons[i][j]), "toggled",
                            GTK_SIGNAL_FUNC (tictactoe_toggle), ttt);
        gtk_widget_set_usize (ttt->buttons[i][j], 20, 20);
        gtk_widget_show (ttt->buttons[i][j]);
      }
}


GtkWidget*
tictactoe_new ()
{
  return GTK_WIDGET ( gtk_type_new (tictactoe_get_type ()));
}

void           
tictactoe_clear (Tictactoe *ttt)
{
  int i,j;

  for (i=0;i<3;i++)
    for (j=0;j<3;j++)
      {
        gtk_signal_handler_block_by_data (GTK_OBJECT(ttt->buttons[i][j]), ttt);
        gtk_toggle_button_set_state (GTK_TOGGLE_BUTTON (ttt->buttons[i][j]),
                                     FALSE);
        gtk_signal_handler_unblock_by_data (GTK_OBJECT(ttt->buttons[i][j]), ttt);
      }
}

static void
tictactoe_toggle (GtkWidget *widget, Tictactoe *ttt)
{
  int i,k;

  static int rwins[8][3] = { { 0, 0, 0 }, { 1, 1, 1 }, { 2, 2, 2 },
                             { 0, 1, 2 }, { 0, 1, 2 }, { 0, 1, 2 },
                             { 0, 1, 2 }, { 0, 1, 2 } };
  static int cwins[8][3] = { { 0, 1, 2 }, { 0, 1, 2 }, { 0, 1, 2 },
                             { 0, 0, 0 }, { 1, 1, 1 }, { 2, 2, 2 },
                             { 0, 1, 2 }, { 2, 1, 0 } };

  int success, found;

  for (k=0; k<8; k++)
    {
      success = TRUE;
      found = FALSE;

      for (i=0;i<3;i++)
        {
          success = success && 
            GTK_TOGGLE_BUTTON(ttt->buttons[rwins[k][i]][cwins[k][i]])->active;
          found = found ||
            ttt->buttons[rwins[k][i]][cwins[k][i]] == widget;
        }
      
      if (success && found)
        {
          gtk_signal_emit (GTK_OBJECT (ttt), 
                           tictactoe_signals[TICTACTOE_SIGNAL]);
          break;
        }
    }
}

最後, 使用Tictactoe widget的范例程式:

#include <gtk/gtk.h>
#include "tictactoe.h"

/* Invoked when a row, column or diagonal is completed */
void
win (GtkWidget *widget, gpointer data)
{
  g_print ("Yay!\n");
  tictactoe_clear (TICTACTOE (widget));
}

int 
main (int argc, char *argv[])
{
  GtkWidget *window;
  GtkWidget *ttt;
  
  gtk_init (&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  
  gtk_window_set_title (GTK_WINDOW (window), "Aspect Frame");
  
  gtk_signal_connect (GTK_OBJECT (window), "destroy",
                      GTK_SIGNAL_FUNC (gtk_exit), NULL);
  
  gtk_container_border_width (GTK_CONTAINER (window), 10);

  /* Create a new Tictactoe widget */
  ttt = tictactoe_new ();
  gtk_container_add (GTK_CONTAINER (window), ttt);
  gtk_widget_show (ttt);

  /* And attach to its "tictactoe" signal */
  gtk_signal_connect (GTK_OBJECT (ttt), "tictactoe",
                      GTK_SIGNAL_FUNC (win), NULL);

  gtk_widget_show (window);
  
  gtk_main ();
  
  return 0;
}

20.4 从草稿中产生物件.

基本

我们的物件看起来会有点像Tictactoe物件.

/* GTK - The GIMP Toolkit
 * Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#ifndef __GTK_DIAL_H__
#define __GTK_DIAL_H__

#include <gdk/gdk.h>
#include <gtk/gtkadjustment.h>
#include <gtk/gtkwidget.h>


#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */


#define GTK_DIAL(obj)          GTK_CHECK_CAST (obj, gtk_dial_get_type (), GtkDial)
#define GTK_DIAL_CLASS(klass)  GTK_CHECK_CLASS_CAST (klass, gtk_dial_get_type (), GtkDialClass)
#define GTK_IS_DIAL(obj)       GTK_CHECK_TYPE (obj, gtk_dial_get_type ())


typedef struct _GtkDial        GtkDial;
typedef struct _GtkDialClass   GtkDialClass;

struct _GtkDial
{
  GtkWidget widget;

  /* update policy (GTK_UPDATE_[CONTINUOUS/DELAYED/DISCONTINUOUS]) */
  guint policy : 2;

  /* Button currently pressed or 0 if none */
  guint8 button;

  /* Dimensions of dial components */
  gint radius;
  gint pointer_width;

  /* ID of update timer, or 0 if none */
  guint32 timer;

  /* Current angle */
  gfloat angle;

  /* Old values from adjustment stored so we know when something changes */
  gfloat old_value;
  gfloat old_lower;
  gfloat old_upper;

  /* The adjustment object that stores the data for this dial */
  GtkAdjustment *adjustment;
};

struct _GtkDialClass
{
  GtkWidgetClass parent_class;
};


GtkWidget*     gtk_dial_new                    (GtkAdjustment *adjustment);
guint          gtk_dial_get_type               (void);
GtkAdjustment* gtk_dial_get_adjustment         (GtkDial      *dial);
void           gtk_dial_set_update_policy      (GtkDial      *dial,
                                                GtkUpdateType  policy);

void           gtk_dial_set_adjustment         (GtkDial      *dial,
                                                GtkAdjustment *adjustment);
#ifdef __cplusplus
}
#endif /* __cplusplus */


#endif /* __GTK_DIAL_H__ */

在您产生视窗後, 我们设定其型态及背景, 并放指标到物件的GdkWindow使用者资料栏上 最後一步允许GTK来分派事件给各别的物件.

static void
gtk_dial_realize (GtkWidget *widget)
{
  GtkDial *dial;
  GdkWindowAttr attributes;
  gint attributes_mask;

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

  GTK_WIDGET_SET_FLAGS (widget, GTK_REALIZED);
  dial = GTK_DIAL (widget);

  attributes.x = widget->allocation.x;
  attributes.y = widget->allocation.y;
  attributes.width = widget->allocation.width;
  attributes.height = widget->allocation.height;
  attributes.wclass = GDK_INPUT_OUTPUT;
  attributes.window_type = GDK_WINDOW_CHILD;
  attributes.event_mask = gtk_widget_get_events (widget) | 
    GDK_EXPOSURE_MASK | GDK_BUTTON_PRESS_MASK | 
    GDK_BUTTON_RELEASE_MASK | GDK_POINTER_MOTION_MASK |
    GDK_POINTER_MOTION_HINT_MASK;
  attributes.visual = gtk_widget_get_visual (widget);
  attributes.colormap = gtk_widget_get_colormap (widget);

  attributes_mask = GDK_WA_X | GDK_WA_Y | GDK_WA_VISUAL | GDK_WA_COLORMAP;
  widget->window = gdk_window_new (widget->parent->window, &attributes, attributes_mask);

  widget->style = gtk_style_attach (widget->style, widget->window);

  gdk_window_set_user_data (widget->window, widget);

  gtk_style_set_background (widget->style, widget->window, GTK_STATE_ACTIVE);
}

大小的设定

在所有视窗被显示出来之前, GTK会先问每个子物件的大小. 该事件是由gtk_dial_size_request()所处理的. 既然我们的物件不是container物件, 而且没什麽大小约束, 就用个合理的数字就行了.

static void 
gtk_dial_size_request (GtkWidget      *widget,
                       GtkRequisition *requisition)
{
  requisition->width = DIAL_DEFAULT_SIZE;
  requisition->height = DIAL_DEFAULT_SIZE;
}

最後所有物件都有理想的大小. 一般会尽可能用原定大小, 但使用者会改变它的大小. 大小的改变是由gtk_dial_size_allocate().

static void
gtk_dial_size_allocate (GtkWidget     *widget,
                        GtkAllocation *allocation)
{
  GtkDial *dial;

  g_return_if_fail (widget != NULL);
  g_return_if_fail (GTK_IS_DIAL (widget));
  g_return_if_fail (allocation != NULL);

  widget->allocation = *allocation;
  if (GTK_WIDGET_REALIZED (widget))
    {
      dial = GTK_DIAL (widget);

      gdk_window_move_resize (widget->window,
                              allocation->x, allocation->y,
                              allocation->width, allocation->height);

      dial->radius = MAX(allocation->width,allocation->height) * 0.45;
      dial->pointer_width = dial->radius / 5;
    }
}
.

gtk_dial_expose()

就如之前所提到的一样, 所有物件的绘出都是由expose事件来处理. 没什麽可多提的, 除了用gtk_draw_polygon 来画出三维阴影.

static gint
gtk_dial_expose (GtkWidget      *widget,
                 GdkEventExpose *event)
{
  GtkDial *dial;
  GdkPoint points[3];
  gdouble s,c;
  gdouble theta;
  gint xc, yc;
  gint tick_length;
  gint i;

  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  if (event->count > 0)
    return FALSE;
  
  dial = GTK_DIAL (widget);

  gdk_window_clear_area (widget->window,
                         0, 0,
                         widget->allocation.width,
                         widget->allocation.height);

  xc = widget->allocation.width/2;
  yc = widget->allocation.height/2;

  /* Draw ticks */

  for (i=0; i<25; i++)
    {
      theta = (i*M_PI/18. - M_PI/6.);
      s = sin(theta);
      c = cos(theta);

      tick_length = (i%6 == 0) ? dial->pointer_width : dial->pointer_width/2;
      
      gdk_draw_line (widget->window,
                     widget->style->fg_gc[widget->state],
                     xc + c*(dial->radius - tick_length),
                     yc - s*(dial->radius - tick_length),
                     xc + c*dial->radius,
                     yc - s*dial->radius);
    }

  /* Draw pointer */

  s = sin(dial->angle);
  c = cos(dial->angle);


  points[0].x = xc + s*dial->pointer_width/2;
  points[0].y = yc + c*dial->pointer_width/2;
  points[1].x = xc + c*dial->radius;
  points[1].y = yc - s*dial->radius;
  points[2].x = xc - s*dial->pointer_width/2;
  points[2].y = yc - c*dial->pointer_width/2;

  gtk_draw_polygon (widget->style,
                    widget->window,
                    GTK_STATE_NORMAL,
                    GTK_SHADOW_OUT,
                    points, 3,
                    TRUE);
  
  return FALSE;
}

事件处理

最後一段程式处理各种事件, 跟我们之前所做的没有什麽太大的不同. 有两种事件会发生, 使用者滑鼠的动作及其它因素所造成的物件参数调整.

当使用者在物件上按钮时, 我们检查是否靠近我们的指标, 如果是, 将资料存到button一栏, 并用gtk_grab_add()将所有滑鼠事件抓住. 接下来的滑鼠的动作将会被gtk_dial_update_mouse所接管.. 接下来就看我们是如何做的, "value_changed"事件可以用(GTK_UPDATE_CONTINUOUS)来产生, 或用gtk_timeout_add()来延迟一下(GTK_UPDATE_DELAYED), 或仅在按钮按下时反应(GTK_UPDATE_DISCONTINUOUS).

static gint
gtk_dial_button_press (GtkWidget      *widget,
                       GdkEventButton *event)
{
  GtkDial *dial;
  gint dx, dy;
  double s, c;
  double d_parallel;
  double d_perpendicular;

  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  dial = GTK_DIAL (widget);

  /* Determine if button press was within pointer region - we 
     do this by computing the parallel and perpendicular distance of
     the point where the mouse was pressed from the line passing through
     the pointer */
  
  dx = event->x - widget->allocation.width / 2;
  dy = widget->allocation.height / 2 - event->y;
  
  s = sin(dial->angle);
  c = cos(dial->angle);
  
  d_parallel = s*dy + c*dx;
  d_perpendicular = fabs(s*dx - c*dy);
  
  if (!dial->button &&
      (d_perpendicular < dial->pointer_width/2) &&
      (d_parallel > - dial->pointer_width))
    {
      gtk_grab_add (widget);

      dial->button = event->button;

      gtk_dial_update_mouse (dial, event->x, event->y);
    }

  return FALSE;
}

static gint
gtk_dial_button_release (GtkWidget      *widget,
                          GdkEventButton *event)
{
  GtkDial *dial;

  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  dial = GTK_DIAL (widget);

  if (dial->button == event->button)
    {
      gtk_grab_remove (widget);

      dial->button = 0;

      if (dial->policy == GTK_UPDATE_DELAYED)
        gtk_timeout_remove (dial->timer);
      
      if ((dial->policy != GTK_UPDATE_CONTINUOUS) &&
          (dial->old_value != dial->adjustment->value))
        gtk_signal_emit_by_name (GTK_OBJECT (dial->adjustment), "value_changed");
    }

  return FALSE;
}

static gint
gtk_dial_motion_notify (GtkWidget      *widget,
                         GdkEventMotion *event)
{
  GtkDial *dial;
  GdkModifierType mods;
  gint x, y, mask;

  g_return_val_if_fail (widget != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (widget), FALSE);
  g_return_val_if_fail (event != NULL, FALSE);

  dial = GTK_DIAL (widget);

  if (dial->button != 0)
    {
      x = event->x;
      y = event->y;

      if (event->is_hint || (event->window != widget->window))
        gdk_window_get_pointer (widget->window, &x, &y, &mods);

      switch (dial->button)
        {
        case 1:
          mask = GDK_BUTTON1_MASK;
          break;
        case 2:
          mask = GDK_BUTTON2_MASK;
          break;
        case 3:
          mask = GDK_BUTTON3_MASK;
          break;
        default:
          mask = 0;
          break;
        }

      if (mods & mask)
        gtk_dial_update_mouse (dial, x,y);
    }

  return FALSE;
}

static gint
gtk_dial_timer (GtkDial *dial)
{
  g_return_val_if_fail (dial != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_DIAL (dial), FALSE);

  if (dial->policy == GTK_UPDATE_DELAYED)
    gtk_signal_emit_by_name (GTK_OBJECT (dial->adjustment), "value_changed");

  return FALSE;
}

static void
gtk_dial_update_mouse (GtkDial *dial, gint x, gint y)
{
  gint xc, yc;
  gfloat old_value;

  g_return_if_fail (dial != NULL);
  g_return_if_fail (GTK_IS_DIAL (dial));

  xc = GTK_WIDGET(dial)->allocation.width / 2;
  yc = GTK_WIDGET(dial)->allocation.height / 2;

  old_value = dial->adjustment->value;
  dial->angle = atan2(yc-y, x-xc);

  if (dial->angle < -M_PI/2.)
    dial->angle += 2*M_PI;

  if (dial->angle < -M_PI/6)
    dial->angle = -M_PI/6;

  if (dial->angle > 7.*M_PI/6.)
    dial->angle = 7.*M_PI/6.;

  dial->adjustment->value = dial->adjustment->lower + (7.*M_PI/6 - dial->angle) *
    (dial->adjustment->upper - dial->adjustment->lower) / (4.*M_PI/3.);

  if (dial->adjustment->value != old_value)
    {
      if (dial->policy == GTK_UPDATE_CONTINUOUS)
        {
          gtk_signal_emit_by_name (GTK_OBJECT (dial->adjustment), "value_changed");
        }
      else
        {
          gtk_widget_draw (GTK_WIDGET(dial), NULL);

          if (dial->policy == GTK_UPDATE_DELAYED)
            {
              if (dial->timer)
                gtk_timeout_remove (dial->timer);

              dial->timer = gtk_timeout_add (SCROLL_DELAY_LENGTH,
                                             (GtkFunction) gtk_dial_timer,
                                             (gpointer) dial);
            }
        }
    }
}

static void
gtk_dial_update (GtkDial *dial)
{
  gfloat new_value;
  
  g_return_if_fail (dial != NULL);
  g_return_if_fail (GTK_IS_DIAL (dial));

  new_value = dial->adjustment->value;
  
  if (new_value < dial->adjustment->lower)
    new_value = dial->adjustment->lower;

  if (new_value > dial->adjustment->upper)
    new_value = dial->adjustment->upper;

  if (new_value != dial->adjustment->value)
    {
      dial->adjustment->value = new_value;
      gtk_signal_emit_by_name (GTK_OBJECT (dial->adjustment), "value_changed");
    }

  dial->angle = 7.*M_PI/6. - (new_value - dial->adjustment->lower) * 4.*M_PI/3. /
    (dial->adjustment->upper - dial->adjustment->lower);

  gtk_widget_draw (GTK_WIDGET(dial), NULL);
}

static void
gtk_dial_adjustment_changed (GtkAdjustment *adjustment,
                              gpointer       data)
{
  GtkDial *dial;

  g_return_if_fail (adjustment != NULL);
  g_return_if_fail (data != NULL);

  dial = GTK_DIAL (data);

  if ((dial->old_value != adjustment->value) ||
      (dial->old_lower != adjustment->lower) ||
      (dial->old_upper != adjustment->upper))
    {
      gtk_dial_update (dial);

      dial->old_value = adjustment->value;
      dial->old_lower = adjustment->lower;
      dial->old_upper = adjustment->upper;
    }
}

static void
gtk_dial_adjustment_value_changed (GtkAdjustment *adjustment,
                                    gpointer       data)
{
  GtkDial *dial;

  g_return_if_fail (adjustment != NULL);
  g_return_if_fail (data != NULL);

  dial = GTK_DIAL (data);

  if (dial->old_value != adjustment->value)
    {
      gtk_dial_update (dial);

      dial->old_value = adjustment->value;
    }
}

有可能的增强之处

这个Dial物件到目前为止有670行. 这看起来好像有不少了, 不过我们真正完成的只有一点点, 因为大部份都是标头及模子. 还是有许多可以加强的地方:

20.5 更多一点

关於产生一个新的物件的细部资讯在以上被提供出来. 如果您想要写一个属於自己的物件, 我想最好的范例就是GTK本身了.

问问您自己一些关於您想要写的物件:

它是否是个Container物件?
它是否有自己的视窗?
是否是个现有物件的修改?
找出一个相近的物件, 然後开始动工.
祝好运!

20.6 版权

This section on of the tutorial on writing widgets is Copyright (C) 1997 Owen Taylor

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.


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