设计模式之策略设计模式

问题引入:在一些购物系统,可能会在搞一些促销，比如满多少减多少,全场打折等,那这样的怎么设计比较好呢？这时策略模式就是一个很好的解决方法。

1.定义

定义了一系列的算法，并将每一个算法封装起来，而且使它们还可以相互替换。策略模式让算法独立于使用它的客户而独立变化。

2.UML类图

3.实现

1、定义baseStrategy接口CashBase

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
@protocol CashBase <NSObject>
-(CGFloat)acceptCash:(CGFloat)cash;
@end

2.定义Strategy接口子类CashNormal

#import <Foundation/Foundation.h>
#import "CashBase.h"

@interface CashNormal : NSObject<CashBase>

@end

#import "CashNormal.h"

@implementation CashNormal

-(CGFloat)acceptCash:(CGFloat)cash{
    return cash;
}
@end

 定义子类CashRobate

#import <Foundation/Foundation.h>
#import "CashBase.h"
@interface CashRobate : NSObject<CashBase>
-(instancetype)initWithMoneyRebate:(CGFloat)moneyRebate;
@end

#import "CashRobate.h"

@interface CashRobate ()
@property(nonatomic)CGFloat moneyRebate;
@end

@implementation CashRobate
-(instancetype)initWithMoneyRebate:(CGFloat)moneyRebate{
    self = [super init];
    if (self) {
        _moneyRebate = moneyRebate;
    }
    return self;
}

-(CGFloat)acceptCash:(CGFloat)cash{
    return self.moneyRebate * cash;
}

@end

定义子类CaseReturn

#import <Foundation/Foundation.h>
#import "CashBase.h"
@interface CaseReturn : NSObject<CashBase>
-(instancetype)initWithMoneyCondition:(CGFloat)moneyCondition moneyReturn:(CGFloat)moneyReturn;
@end

#import "CaseReturn.h"

@interface CaseReturn ()
@property(nonatomic)CGFloat moneyCondition;
@property(nonatomic)CGFloat moneyReturn;
@end

@implementation CaseReturn
-(instancetype)initWithMoneyCondition:(CGFloat)moneyCondition moneyReturn:(CGFloat)moneyReturn{
    self = [super init];
    if (self) {
        _moneyCondition = moneyCondition;
        _moneyReturn = moneyReturn;
    }
    return self;
}
-(CGFloat)acceptCash:(CGFloat)cash{
    return self.moneyCondition - self.moneyReturn;
}
@end

定义context

#import <Foundation/Foundation.h>
#import "CashBase.h"
@interface CashContext : NSObject
-(instancetype)initWithCashSuper:(id<CashBase>)cashBase;
-(CGFloat)getResult:(CGFloat)money;
@end

#import "CashContext.h"

@interface CashContext()
@property(strong,nonatomic) id<CashBase> cashSuper;
@end

@implementation CashContext
-(instancetype)initWithCashSuper:(id<CashBase>)cashBase{
    self = [super init];
    if (self) {
        self.cashSuper = cashBase;
    }
    return self;
}
-(CGFloat)getResult:(CGFloat)money{
    return [self.cashSuper acceptCash:money];
}
@end

4.调用

CashRobate *robate = [[CashRobate alloc]initWithMoneyRebate:0.8];
    CashContext *context = [[CashContext alloc]initWithCashSuper:robate];
    NSLog(@"结果是%f",[context getResult:100]);
    
    CaseReturn *cashReturn = [[CaseReturn alloc]initWithMoneyCondition:300 moneyReturn:100];
    CashContext *contextReturn = [[CashContext alloc]initWithCashSuper:cashReturn];
    NSLog(@"结果是%f",[contextReturn getResult:0]);

5.输出