Glib學習筆記（四）

你將學到什麼

使用GObject模擬實現接口

使用接口

• 首先按照學習筆記（一）定義一個普通的GObject類
• 使用G_DEFINE_TYPE_WITH_CODE和G_IMPLEMENT_INTERFACE替代G_DEFINE_TYPE來實現類定義

static void viewer_file_editable_interface_init (ViewerEditableInterface *iface);

G_DEFINE_TYPE_WITH_CODE (ViewerFile, viewer_file, G_TYPE_OBJECT,
                         G_IMPLEMENT_INTERFACE (VIEWER_TYPE_EDITABLE,
                                                viewer_file_editable_interface_init))

• 實現接口初始化函數viewer_file_editable_interface_init，接口內聲明的每一個虛函數指針都要被賦予實現

static void
viewer_file_editable_save (ViewerFile  *self,
                           GError     **error)
{
  g_print ("File implementation of editable interface save method: %s.\n",
           self->filename);
}

static void
viewer_file_editable_undo (ViewerFile *self,
                           guint       n_steps)
{
  g_print ("File implementation of editable interface undo method: %s.\n",
           self->filename);
}

static void
viewer_file_editable_redo (ViewerFile *self,
                           guint       n_steps)
{
  g_print ("File implementation of editable interface redo method: %s.\n",
           self->filename);
}

static void
viewer_file_editable_interface_init (ViewerEditableInterface *iface)
{
  iface->save = viewer_file_editable_save;
  iface->undo = viewer_file_editable_undo;
  iface->redo = viewer_file_editable_redo;
}

static void
viewer_file_init (ViewerFile *self)
{
  /* Instance variable initialisation code. */
}

擴展接口

若是一個接口的實現依賴另外一個接口的實現，有點相似繼承，那麼首先按照上面的方式實現兩個接口的定義，而後在定義GType的時候依次使用G_IMPLEMENT_INTERFACE添加兩個接口的實現。

/* Make the ViewerEditableLossy interface require ViewerEditable interface. */
G_DEFINE_INTERFACE (ViewerEditableLossy, viewer_editable_lossy, VIEWER_TYPE_EDITABLE);

static void
viewer_file_editable_lossy_compress (ViewerEditableLossy *editable)
{
  ViewerFile *self = VIEWER_FILE (editable);

  g_print ("File implementation of lossy editable interface compress method: %s.\n",
           self->filename);
}

static void
viewer_file_editable_lossy_interface_init (ViewerEditableLossyInterface *iface)
{
  iface->compress = viewer_file_editable_lossy_compress;
}

static void
viewer_file_editable_save (ViewerEditable  *editable,
                           GError         **error)
{
  ViewerFile *self = VIEWER_FILE (editable);

  g_print ("File implementation of editable interface save method: %s.\n",
           self->filename);
}

static void
viewer_file_editable_undo (ViewerEditable *editable,
                           guint           n_steps)
{
  ViewerFile *self = VIEWER_FILE (editable);

  g_print ("File implementation of editable interface undo method: %s.\n",
           self->filename);
}

static void
viewer_file_editable_redo (ViewerEditable *editable,
                           guint           n_steps)
{
  ViewerFile *self = VIEWER_FILE (editable);

  g_print ("File implementation of editable interface redo method: %s.\n",
           self->filename);
}

static void
viewer_file_editable_interface_init (ViewerEditableInterface *iface)
{
  iface->save = viewer_file_editable_save;
  iface->undo = viewer_file_editable_undo;
  iface->redo = viewer_file_editable_redo;
}

static void
viewer_file_class_init (ViewerFileClass *klass)
{
  /* Nothing here. */
}

static void
viewer_file_init (ViewerFile *self)
{
  /* Instance variable initialisation code. */
}

G_DEFINE_TYPE_WITH_CODE (ViewerFile, viewer_file, G_TYPE_OBJECT,
                         G_IMPLEMENT_INTERFACE (VIEWER_TYPE_EDITABLE,
                         viewer_file_editable_interface_init)
                         G_IMPLEMENT_INTERFACE (VIEWER_TYPE_EDITABLE_LOSSY,
                         viewer_file_editable_lossy_interface_init))

接口屬性

接口一樣也能夠擁有屬性，不過是使用g_object_interface_install_property函數而不是像定義GType同樣使用g_object_class_install_property函數來安裝屬性，以下所示：

static void
viewer_editable_default_init (ViewerEditableInterface *iface)
{
    g_object_interface_install_property (iface,
                                        g_param_spec_double ("autosave-frequency",
                                        "Autosave frequency",
                                        "Frequency (in per-seconds) to autosave backups of the editable content at Or zero to disable autosaves.",
                                        0.0,  /* minimum */
                                        G_MAXDOUBLE,  /* maximum */
                                        0.0,  /* default */
                                        G_PARAM_READWRITE));
}

須要值得注意的一點是

重寫接口方法

ViewerAudioFile繼承自ViewerFile，二者都實現了ViewerEditable接口。ViewerAudioFile僅實現了ViewerEditable接口的其中一個方法，其餘接口方法使用基類ViewerFile的實現，以下所示：

static void
viewer_audio_file_editable_save (ViewerEditable  *editable,
                                 GError         **error)
{
  ViewerAudioFile *self = VIEWER_AUDIO_FILE (editable);

  g_print ("Audio file implementation of editable interface save method.\n");
}

static void
viewer_audio_file_editable_interface_init (ViewerEditableInterface *iface)
{
  /* Override the implementation of save(). */
  iface->save = viewer_audio_file_editable_save;

  /*
   * Leave iface->undo and ->redo alone, they are already set to the
   * base class implementation.
   */
}

G_DEFINE_TYPE_WITH_CODE (ViewerAudioFile, viewer_audio_file, VIEWER_TYPE_FILE,
                         G_IMPLEMENT_INTERFACE (VIEWER_TYPE_EDITABLE,
                                                viewer_audio_file_editable_interface_init))

static void
viewer_audio_file_class_init (ViewerAudioFileClass *klass)
{
  /* Nothing here. */
}

static void
viewer_audio_file_init (ViewerAudioFile *self)
{
  /* Nothing here. */
}

在接口的default_init函數裏面使用g_type_interface_peek_parent函數能夠獲取基類的接口實現，可將其保存到全局變量中供其餘函數使用。下面的例子中，ViewerAudioFile重寫了接口的save函數，並在重寫函數中直接調用基類ViewerFile接口的save函數實現。

static ViewerEditableInterface *viewer_editable_parent_interface = NULL;

static void
viewer_audio_file_editable_save (ViewerEditable  *editable,
                                 GError         **error)
{
  ViewerAudioFile *self = VIEWER_AUDIO_FILE (editable);

  g_print ("Audio file implementation of editable interface save method.\n");

  /* Now call the base implementation */
  viewer_editable_parent_interface->save (editable, error);
}

static void
viewer_audio_file_editable_interface_init (ViewerEditableInterface *iface)
{
  viewer_editable_parent_interface = g_type_interface_peek_parent (iface);

  iface->save = viewer_audio_file_editable_save;
}

G_DEFINE_TYPE_WITH_CODE (ViewerAudioFile, viewer_audio_file, VIEWER_TYPE_FILE,
                         G_IMPLEMENT_INTERFACE (VIEWER_TYPE_EDITABLE,
                                                viewer_audio_file_editable_interface_init))

static void
viewer_audio_file_class_init (ViewerAudioFileClass *klass)
{
  /* Nothing here. */
}

static void
viewer_audio_file_init (ViewerAudioFile *self)
{
  /* Nothing here. */
}