GObject：自定义类创建实例（继承、重载）

概述

本文旨在介绍GObject如何自定义新类，GObject的一些基础概念（类、对象、实例）可参考【GObject 对象-类-实例概念介绍】。

正文

GObject提供了丰富的宏定义，使用G_DEFINE_TYPE 宏定义可以帮助我们快速的定义一个新的类。当然如果不想借助这个宏定义，则可以自己实现XXX_get_type()函数，并在此函数内调用g_type_register_static() 注册新的类。我们在使用g_object_new函数创建刚才注册的类时，第一个参数就是XXX_get_type( )。而XXX_get_type( )就是实现向GObject注册新的类（与自己调用g_type_register_static接口进行注册是一样的）的入口。而G_DEFINE_TYPE的本质只是帮我们定义好了XXX_get_type( )的实现。

如下代码含义：

• 参数1 “Shape”：注册新的类名称（与结构体同名）
• 参数2 “shape”：注册新类初始化函数前缀，比如shape_init(Shape *shape)。这里填写什么字符串（假设为：XXX），就要实现XXX_init，XXX_class_init，XXX_get_type。
• 参数3 “G_TYPE_OBJECT”：父类的类型，这里表示Shape的父类是OBJECT。其实就是对应父类的XXX_get_type。

G_DEFINE_TYPE(Shape, shape, G_TYPE_OBJECT);

定义一个新的类，最少要实现三个函数：

/* 类结构 */
typedef struct _mytest {
	int member1;
	char member2;
	void (*func)(void);
	/*  略 */
} Mytest;

//对象初始化函数
void mytest_init(Mytest *arg);
//类的初始化函数
void mytest_class_init(MytestClass *class);
//该函数实现向GObject注册我们新定义的mytest类，可通过G_DEFINE_TYPE进行实现。
Gtype mytest_get_type(void)

接下来我们展示一个Demo，该Demo实现了一个shape类和一个square类，square类继承了shape类，并且重载了shape类的info()函数。

shape.h代码：

#ifndef _SHAPE_H_
#define _SHAPE_H_

#include 

/* define new class type. */
#define SHAPE_TYPE (shape_get_type())
/* Gobject* to Shape* */
#define SHAPE(obj) (G_TYPE_CHECK_INSTANCE_CAST((obj), SHAPE_TYPE, Shape))

typedef struct _Shape Shape;
typedef struct _ShapeClass ShapeClass;

struct _Shape {
    GObject parent;
    gint type;
    gchar *name;
    void (*info)(void);
};

struct _ShapeClass {
    GObjectClass parent_class;
};

/* xxx_init() xxx_class_init() xxx_get_type() must exist */
GType shape_get_type(void);
gchar *shape_get_name(Shape *shape);

#endif // _SHAPE_H_

shape.c代码：

#include "shape.h"

/* very importent!!! */
G_DEFINE_TYPE(Shape, shape, G_TYPE_OBJECT);

static void shape_info(void) {
	g_print("+++++ This is a shape type +++++\n");
}

static void shape_init(Shape *shape)
{
	g_print("+++++ %s is called! +++++\n", __func__);
    shape->name = "shape";
    shape->type = 0;
    shape->info = shape_info;
}

static void shape_class_init(ShapeClass *class)
{
	g_print("+++++ %s is called! +++++\n", __func__);
}

char *shape_get_name(Shape *shape)
{
	g_print("+++++ shape name: %s +++++\n", shape->name);
}

square.h代码：

#ifndef _SUEQRE_H_
#define _SUEQRE_H_

#include "shape.h"

/* define new class type. */
#define SQUARE_TYPE (square_get_type())
/* Gobject* to Square* */
#define SQUARE(obj) (G_TYPE_CHECK_INSTANCE_CAST((obj), SQUARE_TYPE, Square))

typedef struct _Square Square;
typedef struct _SquareClass SquareClass;

struct _Square {
    Shape parent;
    gint width;
	gint height;
};

struct _SquareClass {
    ShapeClass parent_class;
};

/* xxx_init() xxx_class_init() xxx_get_type() must exist */
GType square_get_type(void);
gint square_set_wh(Square *square, gint w, gint h);
gint square_get_area(Square *square);

#endif // _SUEQRE_H_

square.c代码：

#include "square.h"

/* very importent!!! */
G_DEFINE_TYPE(Square, square, SHAPE_TYPE);

static void shape_info(void) {
	g_print("+++++ This is a square type +++++\n");
}

static void square_init(Square *square)
{
	Shape *shape = SHAPE(square);

	g_print("+++++ %s is called! +++++\n", __func__);
    shape->name = "shape";
    shape->type = 0;
    shape->info = shape_info;

	square->width = 0;
	square->height = 0;
}

static void square_class_init(SquareClass *class)
{
	g_print("+++++ %s is called! +++++\n", __func__);
}

gint square_set_wh(Square *square, gint w, gint h)
{
	g_print("+++++ %s is called! +++++\n", __func__);
	square->width = w;
	square->height = h;
}

gint square_get_area(Square *square)
{
	g_print("+++++ %s is called! +++++\n", __func__);
	return square->width * square->height;
}

main.c代码：

#include 

#include "shape.h"
#include "square.h"

int main(int argc, char *argv[])
{
	Shape *shape = NULL;
	Square *square = NULL;

	g_print("Shape info:\n");
	shape = g_object_new(SHAPE_TYPE, NULL);
	shape->info();
	g_print("\n");

	g_print("Square info:\n");
	square = g_object_new(SQUARE_TYPE, NULL);
	SHAPE(square)->info();
	square_set_wh(square, 3, 2);
	g_print("area:%d\n", square_get_area(square));

    return TRUE;
}

运行结果：

完整工程地址如下（包含Makefile）：
https://download.csdn.net/download/lyy901135/11424214