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。

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