大话设计模式之策略模式

第二章：商场促销——策略模式

策略模式的定义:

策略模式是一种定义一系列算法的方法，从概念上来看，所有这些算法完成的都是相同的工作，知识实现不同，他可以以相同的方式调用所有的算法，减少了各类算法类与使用算法类之间的耦合

策略模式的优点：

1. 策略模式的Strategy 类层次为Context定义了一些列的可供重用的算法或行为。继承有助于析取这些算法中的公共功能

2.简化了单元测试，因为每个算法都要自己的类，可以通过自己的接口单独测试

当不同的行为堆砌在一个类中时，就很难避免使用条件语句来选择合适的行为，将这些行为封装在一个个独立的Strategy类中，可以在使用这些行为的类中消除条件语句

策略模式就是用来封装算法的，但是在实践中，我们发现可以用它来封装几乎任何类型的规则，只要在分析过程中听到需要在不同实践应用不同的业务规则，就可以考虑使用策略模式处理这种变化的可能性

在基本的策略模式中，选择所用具体实现的职责有客户端对象承担，并转给策略模式的Context对象

父类CashSuper

CashSuper.h

@interface CashSuper : NSObject
-(double)acceptCash:(double)money;
@end

CashSuper.m

@implementation CashSuper

-(double)acceptCash:(double)money{

return money;

}

@end

正常消费类 CashNormal

CashNormal.h

#import <Foundation/Foundation.h>
#import "CashSuper.h"
@interface CashNormal : CashSuper@end

CashNormal.m

#import "CashNormal.h"@implementation CashNormal
-(double)acceptCash:(double)money{return money;
}
@end

打折消费类CashRebate

CashRebate.h

#import <Foundation/Foundation.h>
#import "CashSuper.h"
@interface CashRebate : CashSuper
@property(assign,nonatomic)double Rebate;
-(instancetype)initWithRebate:(double) Rebate;
@end

CashRebate.m

#import "CashRebate.h"@implementation CashRebate
- (instancetype)initWithRebate:(double)Rebate{self = [super init];if (self) {_Rebate=Rebate;}return self;
}
-(double)acceptCash:(double)money{return money*_Rebate;
}
@end

返利消费类CashReturn

CashReturn.h

#import <Foundation/Foundation.h>
#import "CashSuper.h"
@interface CashReturn : CashSuper
@property(assign,nonatomic)double moneyCondition;
@property(assign,nonatomic)double moneyReturn;
-(instancetype)initWithMoneyCondition:(double)moneyCondition :(double)moneyReturn;
@end

CashReturn.m

#import "CashReturn.h"@implementation CashReturn
-(instancetype)initWithMoneyCondition:(double)moneyCondition :(double)moneyReturn
{self = [super init];if (self) {_moneyCondition=moneyCondition;_moneyReturn=moneyReturn;}return self;
}
-(double)acceptCash:(double)money{double result=money;if (money>=_moneyCondition) {result=money-((int)(money/_moneyCondition))*_moneyReturn;}return result;
}
@end

配置类，维护对对象的使用CashContext类

CashContext.h

#import <Foundation/Foundation.h>
#import "CashSuper.h"
@interface CashContext : NSObject
@property(nonatomic,strong)CashSuper *cashsuper;
-(instancetype)initWith:(CashSuper *)csuper;
-(double)GetResult:(double)money;
@end

CashContext.m

#import "CashContext.h"@implementation CashContext
- (instancetype)initWith:(CashSuper *)csuper
{self = [super init];if (self) {_cashsuper=csuper;}return self;
}
-(double)GetResult:(double)money{return  [_cashsuper acceptCash:money];}
@end

主函数

#import <Foundation/Foundation.h>
#import "CashContext.h"
#import "CashSuper.h"
#import "CashNormal.h"
#import "CashRebate.h"
#import "CashReturn.h"
int main(int argc, const char * argv[]) {@autoreleasepool {char type='B';double result=0.0;CashContext *cc=nil;switch (type) {case 'N':cc=[[CashContext alloc]initWith:[[CashNormal alloc]init]];break;case 'B':cc=[[CashContext alloc]initWith:[[CashRebate alloc]initWithRebate:0.7]];break;case 'T':cc=[[CashContext alloc]initWith:[[CashReturn alloc] initWithMoneyCondition:300 :100]];break;}result = [cc GetResult:500];NSLog(@"%f",result);}return 0;
}