1 簡介

簡單工廠方法定義一個用于創(chuàng)建對象的類，該類接受一個參數(shù)，通過參數(shù)決定創(chuàng)建不同的對象。

GOF并沒有把簡單工廠方法定義為23種設計模式之一，可以認為簡單工廠方法是工廠方法的簡化形式。

為了體現(xiàn)簡單工廠方法和工廠方法的區(qū)別和聯(lián)系，此處把簡單工廠方法先單獨講一下。

2 模擬場景

假設你要生產(chǎn)電腦，電腦由硬盤、內(nèi)存條、CPU、主板的部件組成。你為了保證供應鏈可靠，每種部件都選擇了至少兩家供應商。比如： 硬盤供應商 seagate、Toshiba 內(nèi)存條供應商 SAMSUNG、Crucial CPU供應商 intel、AMD 主板供應商 intel、AMD 此處列出多個部件是為了后面講解工廠方法、抽象工廠方法時使用同一個模擬場景。本章講簡單工廠方法暫時不需要涉及這么多部件，所以僅以硬盤這一個部件為例進行講解。

3 實現(xiàn)的思路

硬盤就是要創(chuàng)建的對象（即：產(chǎn)品）。為了讓不同供應商提供的硬盤可以通用，要定義一個硬盤產(chǎn)品類，并讓不同供應商的硬盤都繼承硬盤產(chǎn)品類的接口。

還需要定義一個創(chuàng)建硬盤對象的類（即：工廠）。工廠類根據(jù)參數(shù)決定創(chuàng)建哪家供應商的硬盤對象。

4 實現(xiàn)硬盤對象創(chuàng)建

參與者: （1）Product: HardDisk 定義硬盤對象的接口 （2）Concrete Product: SeagateHardDisk, ToshibaHardDisk 實現(xiàn)不同供應商的硬盤 （3）SimpleFactory: HardDiskFactory 根據(jù)參數(shù)，創(chuàng)建不同供應商的硬盤對象

UML：



HardDisk代碼示例：

hard_disk.h：

#ifndef HARD_DISK_H
#define HARD_DISK_H


struct HardDisk {
    void (*Operation)(struct HardDisk *this);
};


#endif

SeagateHardDisk代碼示例：

seagate_hard_disk.h：

#ifndef SEAGATE_HARD_DISK_H
#define SEAGATE_HARD_DISK_H


#include "hard_disk.h"


struct SeagateHardDisk {
    struct HardDisk hardDisk;
};


// 構造函數(shù)
void SeagateHardDisk(struct SeagateHardDisk *this);


// 析構函數(shù)
void _SeagateHardDisk(struct SeagateHardDisk *this);


#endif

seagate_hard_disk.c：

#include "seagate_hard_disk.h"
#include "stdio.h"


void SeagateOperation(struct SeagateHardDisk *this)
{
    printf("這是 Seagate 硬盤
");
}


void SeagateHardDisk(struct SeagateHardDisk *this)
{
    this->hardDisk.Operation = (void(*)(struct HardDisk *))SeagateOperation;
}


void _SeagateHardDisk(struct SeagateHardDisk *this)
{
    this->hardDisk.Operation = NULL;
}

ToshibaHardDisk代碼示例：

toshiba_hard_disk.h：

#ifndef TOSHIBA_HARD_DISK_H
#define TOSHIBA_HARD_DISK_H


#include "hard_disk.h"


struct ToshibaHardDisk {
    struct HardDisk hardDisk;
};


// 構造函數(shù)
void ToshibaHardDisk(struct ToshibaHardDisk *this);


// 析構函數(shù)
void _ToshibaHardDisk(struct ToshibaHardDisk *this);


#endif

toshiba_hard_disk.c：

#include "toshiba_hard_disk.h"
#include "stdio.h"


void ToshibaOperation(struct ToshibaHardDisk *this)
{
    printf("這是 Toshiba 硬盤
");
}


void ToshibaHardDisk(struct ToshibaHardDisk *this)
{
    this->hardDisk.Operation = (void(*)(struct HardDisk *))ToshibaOperation;
}


void _ToshibaHardDisk(struct ToshibaHardDisk *this)
{
    this->hardDisk.Operation = NULL;
}

HardDiskFactory代碼示例：

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);
};


// 構造函數(shù)
void HardDiskFactory(struct HardDiskFactory *this);


// 析構函數(shù)
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
");
                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
");
                return NULL;
            }
            ToshibaHardDisk(toshibaHardDisk);
            return (struct HardDisk *)toshibaHardDisk;
        }
        default:
            printf("未知的供應商
");
            return NULL;
    }
}


void Destroy(struct HardDiskFactory *this, struct HardDisk* hardDisk)
{
    if (hardDisk != NULL) {
        free(hardDisk);
    }
}


// 構造函數(shù)
void HardDiskFactory(struct HardDiskFactory *this)
{
    this->Create = Create;
    this->Destroy = Destroy;
}


// 析構函數(shù)
void _HardDiskFactory(struct HardDiskFactory *this)
{
    this->Create = NULL;
    this->Destroy = NULL;
}

客戶端代碼示例：

#include "hard_disk.h"
#include "hard_disk_factory.h"
#include "stddef.h"


void main()
{
    struct HardDisk *hardDisk = NULL;


    struct HardDiskFactory hardDiskFactory;
    HardDiskFactory(&hardDiskFactory);
    
    // 創(chuàng)建 seagate 硬盤對象
    hardDisk = hardDiskFactory.Create(&hardDiskFactory, HARD_DISK_SUPPLIER_SEAGATE);
    // 使用 seagate 硬盤對象
    hardDisk->Operation(hardDisk);  
    // 銷毀 seagate 硬盤對象
    hardDiskFactory.Destroy(&hardDiskFactory, hardDisk);       
    
    // 創(chuàng)建 toshiba 硬盤對象
    hardDisk = hardDiskFactory.Create(&hardDiskFactory, HARD_DISK_SUPPLIER_TOSHIBA);
    // 使用 seagate 硬盤對象
    hardDisk->Operation(hardDisk);
    // 銷毀 toshiba 硬盤對象
    hardDiskFactory.Destroy(&hardDiskFactory, hardDisk);    
    
    _HardDiskFactory(&hardDiskFactory);
}

客戶端顯示示例：

./hard_disk
這是 Seagate 硬盤
這是 Toshiba 硬盤

審核編輯：湯梓紅