电子产品世界

1 简介

简单工厂方法定义一个用于创建对象的类，该类接受一个参数，通过参数决定创建不同的对象。

GOF并没有把简单工厂方法定义为23种设计模式之一，可以认为简单工厂方法是工厂方法的简化形式。 为了体现简单工厂方法和工厂方法的区别和联系，此处把简单工厂方法先单独讲一下。

2 模拟场景

假设你要生产电脑，电脑由硬盘、内存条、CPU、主板的部件组成。你为了保证供应链可靠，每种部件都选择了至少两家供应商。比如：硬盘供应商 seagate、Toshiba内存条供应商 SAMSUNG、CrucialCPU供应商 intel、AMD主板供应商 intel、AMD 此处列出多个部件是为了后面讲解工厂方法、抽象工厂方法时使用同一个模拟场景。本章讲简单工厂方法暂时不需要涉及这么多部件，所以仅以硬盘这一个部件为例进行讲解。

3 实现的思路

硬盘就是要创建的对象（即：产品）。为了让不同供应商提供的硬盘可以通用，要定义一个硬盘产品类，并让不同供应商的硬盘都继承硬盘产品类的接口。 还需要定义一个创建硬盘对象的类（即：工厂）。工厂类根据参数决定创建哪家供应商的硬盘对象。

4 实现硬盘对象创建

参与者:（1）Product: HardDisk 定义硬盘对象的接口（2）Concrete Product: SeagateHardDisk, ToshibaHardDisk 实现不同供应商的硬盘（3）SimpleFactory: HardDiskFactory 根据参数，创建不同供应商的硬盘对象 UML：

HardDisk代码示例： hard_disk.h：

#ifndef HARD_DISK_H#define HARD_DISK_H struct HardDisk { void (*Operation)(struct HardDisk *this);}; #endif

SeagateHardDisk代码示例： seagate_hard_disk.h：

#ifndef SEAGATE_HARD_DISK_H#define SEAGATE_HARD_DISK_H #include "hard_disk.h" struct SeagateHardDisk { struct HardDisk hardDisk;}; // 构造函数void SeagateHardDisk(struct SeagateHardDisk *this); // 析构函数void _SeagateHardDisk(struct SeagateHardDisk *this); #endif

seagate_hard_disk.c：

#include "seagate_hard_disk.h"#include "stdio.h" void SeagateOperation(struct SeagateHardDisk *this){ printf("这是 Seagate 硬盘\n");} void SeagateHardDisk(struct SeagateHardDisk *this){ this->hardDisk.Operation = (void(*)(struct HardDisk *))SeagateOperation;} void _SeagateHardDisk(struct SeagateHardDisk *this){ this->hardDisk.Operation = NULL;}

ToshibaHardDisk代码示例： toshiba_hard_disk.h：

#ifndef TOSHIBA_HARD_DISK_H#define TOSHIBA_HARD_DISK_H #include "hard_disk.h" struct ToshibaHardDisk { struct HardDisk hardDisk;}; // 构造函数void ToshibaHardDisk(struct ToshibaHardDisk *this); // 析构函数void _ToshibaHardDisk(struct ToshibaHardDisk *this); #endif

toshiba_hard_disk.c：

#include "toshiba_hard_disk.h"#include "stdio.h" void ToshibaOperation(struct ToshibaHardDisk *this){ printf("这是 Toshiba 硬盘\n");} void ToshibaHardDisk(struct ToshibaHardDisk *this){ this->hardDisk.Operation = (void(*)(struct HardDisk *))ToshibaOperation;} void _ToshibaHardDisk(struct ToshibaHardDisk *this){ this->hardDisk.Operation = NULL;}

HardDiskFactory代码示例： hard_disk_factory.h：

#ifndef HARD_DISK_FACTORY_H#define HARD_DISK_FACTORY_H #include "hard_disk.h" enum HARD_DISK_SUPPLIER_E { HARD_DISK_SUPPLIER_SEAGATE, HARD_DISK_SUPPLIER_TOSHIBA}; struct HardDiskFactory { struct HardDisk* (*Create)(struct HardDiskFactory *this, enum HARD_DISK_SUPPLIER_E supplier); void (*Destroy)(struct HardDiskFactory *this, struct HardDisk* hardDisk);}; // 构造函数void HardDiskFactory(struct HardDiskFactory *this); // 析构函数void _HardDiskFactory(struct HardDiskFactory *this); #endif

hard_disk_factory.c：

#include "hard_disk_factory.h" #include "seagate_hard_disk.h" #include "toshiba_hard_disk.h" #include "stdio.h" #include "stdlib.h" struct HardDisk *Create(struct HardDiskFactory *this, enum HARD_DISK_SUPPLIER_E supplier) { switch (supplier) { case HARD_DISK_SUPPLIER_SEAGATE: { struct SeagateHardDisk *seagateHardDisk = NULL; if ((seagateHardDisk = malloc(sizeof(struct SeagateHardDisk))) == NULL) { printf("fail in malloc\n"); return NULL; } SeagateHardDisk(seagateHardDisk); return (struct HardDisk *)seagateHardDisk; } case HARD_DISK_SUPPLIER_TOSHIBA: { struct ToshibaHardDisk *toshibaHardDisk = NULL; if ((toshibaHardDisk = malloc(sizeof(struct ToshibaHardDisk))) == NULL) { printf("fail in malloc\n"); return NULL; } ToshibaHardDisk(toshibaHardDisk); return (struct HardDisk *)toshibaHardDisk; } default: printf("未知的供应商\n"); return NULL; }} void Destroy(struct HardDiskFactory *this, struct HardDisk* hardDisk){ if (hardDisk != NULL) { free(hardDisk); }} // 构造函数void HardDiskFactory(struct HardDiskFactory *this){ this->Create = Create; this->Destroy = Destroy;} // 析构函数void _HardDiskFactory(struct HardDiskFactory *this){ this->Create = NULL; this->Destroy = NULL;}

客户端代码示例：

#include "hard_disk.h"#include "hard_disk_factory.h"#include "stddef.h" void main(){ struct HardDisk *hardDisk = NULL; struct HardDiskFactory hardDiskFactory; HardDiskFactory(&hardDiskFactory); // 创建 seagate 硬盘对象 hardDisk = hardDiskFactory.Create(&hardDiskFactory, HARD_DISK_SUPPLIER_SEAGATE); // 使用 seagate 硬盘对象 hardDisk->Operation(hardDisk); // 销毁 seagate 硬盘对象 hardDiskFactory.Destroy(&hardDiskFactory, hardDisk); // 创建 toshiba 硬盘对象 hardDisk = hardDiskFactory.Create(&hardDiskFactory, HARD_DISK_SUPPLIER_TOSHIBA); // 使用 seagate 硬盘对象 hardDisk->Operation(hardDisk); // 销毁 toshiba 硬盘对象 hardDiskFactory.Destroy(&hardDiskFactory, hardDisk); HardDiskFactory(&hardDiskFactory);}

客户端显示示例：

./hard_disk这是 Seagate 硬盘这是 Toshiba 硬盘