Glib学习笔记（三）

你将学到什么

如何实现Object的方法

Object的方法

Object的public方法

在头文件声明一个函数，然后在源文件中实现函数即可

/* declaration in the header. */
void viewer_file_open (ViewerFile  *self,
                       GError     **error);

/* implementation in the source file */
void
viewer_file_open (ViewerFile  *self,
                  GError     **error)
{
  g_return_if_fail (VIEWER_IS_FILE (self));
  g_return_if_fail (error == NULL || *error == NULL);

  /* do stuff here. */
}

Object的public虚函数

GObject通过函数指针的方式来模拟C++语言的虚函数实现，具体步骤如下：

• 在类结构定义里面设置一个函数指针，然后定义一个public方法（用来调用函数指针）
• 在源文件里实现public方法（核心就是调用函数指针）
• 在基类的class_init函数设虚函数指针，指向函数的实现，或者设置为NULL来模拟纯虚函数（子类必须实现函数并设置设置函数指针）

下面的open就是纯虚函数，close就是虚函数

/* declaration in viewer-file.h. */
#define VIEWER_TYPE_FILE viewer_file_get_type ()
G_DECLARE_DERIVABLE_TYPE (ViewerFile, viewer_file, VIEWER, FILE, GObject)

struct _ViewerFileClass
{
  GObjectClass parent_class;

  /* stuff */
  void (*open) (ViewerFile  *self,
                GError     **error);
  void (*close) (ViewerFile  *self,
                 GError     **error);

  /* Padding to allow adding up to 12 new virtual functions without
   * breaking ABI. */
  gpointer padding[12];
};

void viewer_file_open (ViewerFile  *self,
                       GError     **error);
void viewer_file_close (ViewerFile  *self,
                        GError     **error);

/* implementation in viewer-file.c */
void viewer_file_open (ViewerFile  *self,
                       GError     **error);

static void
viewer_file_real_close (ViewerFile  *self,
                        GError     **error)
{
  /* Default implementation for the virtual method. */
}

static void
viewer_file_class_init (ViewerFileClass *klass)
{
  /* this is not necessary, except for demonstration purposes.
   *
   * pure virtual method: mandates implementation in children.
   */
  klass->open = NULL;

  /* merely virtual method. */
  klass->close = viewer_file_real_close;
}

void
viewer_file_open (ViewerFile  *self,
                  GError     **error)
{
  ViewerFileClass *klass;

  g_return_if_fail (VIEWER_IS_FILE (self));
  g_return_if_fail (error == NULL || *error == NULL);

  klass = VIEWER_FILE_GET_CLASS (self);

  /* if the method is purely virtual, then it is a good idea to
   * check that it has been overridden before calling it, and,
   * depending on the intent of the class, either ignore it silently
   * or warn the user.
   */
  g_return_if_fail (klass->open != NULL);
  klass->open (self, error);
}

void
viewer_file_close (ViewerFile  *self,
                   GError     **error)
{
  ViewerFileClass *klass;

  g_return_if_fail (VIEWER_IS_FILE (self));
  g_return_if_fail (error == NULL || *error == NULL);

  klass = VIEWER_FILE_GET_CLASS (self);
  if (klass->close != NULL)
    klass->close (self, error);
}

Object的private虚函数

只要在头文件不提供调用虚函数指针的public方法就可以了，比如去掉上面代码头文件里的void viewer_file_close(ViewerFile *self, GError **error);函数定义，然后在源文件的函数实现前面加上static关键字限制函数作用域为当前文件即可。