【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\";//  SQLServerNSLog(@\"--------------- SQLServer ---------------\");SQLServerFactory *sqlServerFactory = [[SQLServerFactory alloc] init];[[sqlServerFactory createStaffDB] insertStaff:staff];[[sqlServerFactory createDepartmentDB] insertDepartment:department];//  AccessNSLog(@\"--------------- 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） ===============\");//  SQLServerNSLog(@\"--------------- SQLServer ---------------\");[[DBFactory createStaffDBWithDBType:DBTypeSQLServer] insertStaff:staff];[[DBFactory createDepartmentDBWithDBType:DBTypeSQLServer] insertDepartment:department];//  AccessNSLog(@\"--------------- Access ---------------\");[[DBFactory createStaffDBWithDBType:DBTypeAccess] insertStaff:staff];[[DBFactory createDepartmentDBWithDBType:DBTypeAccess] insertDepartment:department];

执行结果：

执行结果