【iOS-设计模式】创建型之抽象工厂模式

概念

抽象工厂提供一个固定的接口，用于创建一系列有关联或相依存的对象，而不必指定其具体类或其创建的细节。客户端与从工厂得到的具体对象之间没有耦合。

实例

我们以一个员工与部门的例子来实现，首先我们创建员工和部门的数据模型，并各声明一个名称的属性：

~/Model/Staff.h
Staff.h

@interface Staff : NSObject

@property(nonatomic, copy) NSString *staffName;

@end

~/Model/Department.h
Department.h

@interface Department : NSObject

@property(nonatomic, copy) NSString *departmentName;

@end

然后分别创建员工协议和部门协议，分别用于插入到数据库中加入员工和加入部门：

~/Staff/StaffProtocol.h
StaffProtocol.h

@class Staff;
@protocol StaffProtocol <NSObject>

- (void)insertStaff:(Staff *)staff;

@end

~/Department/DepartmentProtocol.h
DepartmentProtocol.h

@class Department;

@protocol DepartmentProtocol <NSObject>

- (void)insertDepartment:(Department *)department;

@end

然后分别创建基于各自协议的 SQLServer数据库数据处理类，实现协议 insert 方法：

~/Staff/SQLServerStaff.h
SQLServerStaff.h

#import <Foundation/Foundation.h>
#import "StaffProtocol.h"
#import "Staff.h"

@interface SQLServerStaff : NSObject <StaffProtocol>

@end

~/Staff/SQLServerStaff.m
SQLServerStaff.m

@implementation SQLServerStaff

- (void)insertStaff:(Staff *)staff {
    NSLog(@"%s 插入员工【%@】",__func__,staff.staffName);
}

@end

~/Department/SQLServerDepartment.h
SQLServerDepartment.h

#import <Foundation/Foundation.h>
#import "DepartmentProtocol.h"
#import "Department.h"

@interface SQLServerDepartment : NSObject <DepartmentProtocol>

@end

~/Department/SQLServerDepartment.m
SQLServerDepartment.m

@implementation SQLServerDepartment

- (void)insertDepartment:(Department *)department {
    NSLog(@"%s 插入【%@】部门",__func__,department.departmentName);
}

@end

同样方式创建 Access 数据库的相应数据处理类。

工厂实现

创建数据库的工厂协议 DBFactoryProtocol，声明两个创建数据库的协议方法：

~/Basic version/DBFactoryProtocol.h

#import "StaffProtocol.h"
#import "DepartmentProtocol.h"

@protocol DBFactoryProtocol <NSObject>

- (id <StaffProtocol>)createStaffDB;

- (id <DepartmentProtocol>)createDepartmentDB;

@end

创建 SQLServer 的工厂类 SQLServerFactory 实现协议方法：

#import "SQLServerFactory.h"
#import "SQLServerStaff.h"
#import "SQLServerDepartment.h"

@implementation SQLServerFactory

- (id <StaffProtocol>)createStaffDB {
    return [[SQLServerStaff alloc] init];
}

- (id <DepartmentProtocol>)createDepartmentDB {
    return [[SQLServerDepartment alloc] init];
}

@end

在创建相应数据库，产出相应遵循相应协议的数据处理类。

同样的方式实现 Access 数据库工厂类。

实际上这里写的有点不好，不应该用协议，使用继承会更为合理。使用继承就不会产生方法的连续调用。

于是实现了以下优化版本：

~/Optimized version/DBFactory.h
DBFactory.h

#import <Foundation/Foundation.h>
#import "StaffProtocol.h"
#import "DepartmentProtocol.h"

typedef NS_ENUM(NSUInteger, DBType) {
    DBTypeSQLServer,
    DBTypeAccess
};

@interface DBFactory : NSObject

+ (id <StaffProtocol>)createStaffDBWithDBType:(DBType)dbType;

+ (id <DepartmentProtocol>)createDepartmentDBWithDBType:(DBType)dbType;

@end

~/Optimized version/DBFactory.m
DBFactory.m

#import "DBFactory.h"

#import "SQLServerStaff.h"
#import "SQLServerDepartment.h"

#import "AccessStaff.h"
#import "AccessDepartment.h"

@implementation DBFactory

+ (id <StaffProtocol>)createStaffDBWithDBType:(DBType)dbType {
    switch (dbType) {
        case DBTypeSQLServer:
            return [[SQLServerStaff alloc] init];
            break;
        case DBTypeAccess:
            return [[AccessStaff alloc] init];
            break;
        default:
            return nil;
            break;
    }
}

+ (id <DepartmentProtocol>)createDepartmentDBWithDBType:(DBType)dbType {
    switch (dbType) {
        case DBTypeSQLServer:
            return [[SQLServerDepartment alloc] init];
            break;
        case DBTypeAccess:
            return [[AccessDepartment alloc] init];
            break;
        default:
            return nil;
            break;
    }
}

@end

调用

//=============== 基础版本（Basic version） ===============
    NSLog(@"=============== 基础版本（Basic version） ===============");
    Staff *staff = [[Staff alloc] init];
    staff.staffName = @"Gavin";
    Department *department = [[Department alloc] init];
    department.departmentName = @"研发";
    
    //  SQLServer
    NSLog(@"--------------- SQLServer ---------------");
    SQLServerFactory *sqlServerFactory = [[SQLServerFactory alloc] init];
    [[sqlServerFactory createStaffDB] insertStaff:staff];
    [[sqlServerFactory createDepartmentDB] insertDepartment:department];
    
    //  Access
    NSLog(@"--------------- Access ---------------");
    AccessFactory *accessFactory = [[AccessFactory alloc] init];
    [[accessFactory createStaffDB] insertStaff:staff];
    [[accessFactory createDepartmentDB] insertDepartment:department];
    
    //=============== 优化版本（Optimized version） ===============
    NSLog(@"=============== 优化版本（Optimized version） ===============");
    
    //  SQLServer
    NSLog(@"--------------- SQLServer ---------------");
    [[DBFactory createStaffDBWithDBType:DBTypeSQLServer] insertStaff:staff];
    [[DBFactory createDepartmentDBWithDBType:DBTypeSQLServer] insertDepartment:department];
    
    //  Access
    NSLog(@"--------------- Access ---------------");
    [[DBFactory createStaffDBWithDBType:DBTypeAccess] insertStaff:staff];
    [[DBFactory createDepartmentDBWithDBType:DBTypeAccess] insertDepartment:department];

执行结果：

执行结果

源码

源码地址：FactoryPatternDemo