iOS开发-状态模式
状态模式允许对象内部状态改变时改变它的行为，对象看起来好像修改了它的类。状态模式看起来和策略模式比较相像，策略模式是将可以互换的行为封装起来，然后通过使用委托的方式，决定使用哪一个行为，状态也是封装行为，不同的是可以将行为委托到当前状态。一个需要从外部设置，一个是内部通过状态变更达到行为变成的目的。 基础知识 状态模式的UML类图: State封装基本的状态行为，我们通过Cotext上下文持有状态子类的实例，外部发起请求，我们就可以委托状态进行处理。地铁里面一般都有自动饮料售卖机，我们将所有的饮料都当做商品来看，我们如果需要买饮料需要两步，投币，取货，如果没有商品还可以退钱三种行为，关于自动售卖机的存在无钱状态，有钱状态，售卖中状态，已售罄状态四种状态，稍微思考一下，可以看下面的具体实现。 设计实战 状态行为基类: @protocol StateProtocol <NSObject> @optional -(void)putMoney; @optional -(void)ejectMoney; @optional -(void)pressButton; @optional -(void)distribute; @end @interface State : NSObject<StateProtocol> @end 售卖机处于无钱状态(NoMoneyState): @protocol NoMoneyDelegate <NSObject> -(void)setCurrentState:(State *)currentState; -(State *)geHasMoneyState; @end //没钱状态 @interface NoMoneyState : State @property (weak,nonatomic) id<NoMoneyDelegate> delegate; @end @implementation NoMoneyState -(void)putMoney{ NSLog(@"NoMoneyState-putMoney:投放钱币"); [self.delegate setCurrentState:[self.delegate geHasMoneyState]]; } -(void)ejectMoney{ NSLog(@"NoMoneyState-ejectMoney:没有投入钱币,无法退钱"); } -(void)pressButton{ NSLog(@"NoMoneyState-pressButton:请先投币"); } -(void)distribute{ NSLog(@"NoMoneyState-pressButton:请投币"); } @end 售卖机处于有钱状态(HasMoneyState): @protocol HasMoneyDelegate <NSObject> -(void)setCurrentState:(State *)currentState; -(State *)getNoMoneyState; -(State *)getSoldState; @end //有钱状态 @interface HasMoneyState : State @property (weak,nonatomic) id<HasMoneyDelegate> delegate; @end @implementation HasMoneyState -(void)putMoney{ NSLog(@"HasMoneyState-putMoney:已经投入了钱，暂不支持投入"); } -(void)ejectMoney{ NSLog(@"HasMoneyState-ejectMoney:退钱,重新设置售卖机为无前状态"); [self.delegate setCurrentState:[self.delegate getNoMoneyState]]; } -(void)pressButton{ NSLog(@"HasMoneyState-pressButton:按钮按下,取货"); [self.delegate setCurrentState:[self.delegate getSoldState]]; } -(void)distribute{ NSLog(@"HasMoneyState-distribute:无法进行取出商品"); } @end 售卖机处于售卖状态: @protocol SoldDelegate <NSObject> -(void)setCurrentState:(State *)currentState; -(void)realseProduct; -(NSInteger)getCurrentCount; -(State *)getNoMoneyState; -(State *)getSoldOutState; @end //售出状态 @interface SoldState : State @property (weak,nonatomic) id<SoldDelegate> delegate; @end @implementation SoldState -(void)putMoney{ NSLog(@"SoldState-putMoney:请稍后,正在进行商品出售"); } -(void)ejectMoney{ NSLog(@"SoldState-putMoney:请稍后,正在进行商品出售,无法退钱"); } -(void)pressButton{ NSLog(@"SoldState-putMoney:请在取出物品之后重新投币"); } -(void)distribute{ [self.delegate realseProduct]; if ([self.delegate getCurrentCount]) { [self.delegate setCurrentState:[self.delegate getNoMoneyState]]; }else{ [self.delegate setCurrentState:[self.delegate getSoldOutState]]; } } @end 售罄状态(SoldOutState)： @protocol SoldOutDelegate <NSObject> -(void)setCurrentState:(State *)currentState; @end //售罄状态 @interface SoldOutState : State @property (weak,nonatomic) id<SoldOutDelegate> delegate; @end @implementation SoldOutState -(void)putMoney{ NSLog(@"SoldOutState-PutMoney:已售罄"); } -(void)ejectMoney{ NSLog(@"SoldOutState-ejectMoney:无法退钱"); } -(void)pressButton{ NSLog(@"SoldOutState-pressButton:无法售出"); } -(void)distribute{ NSLog(@"SoldOutState-distribute:无法分发"); } @end 售卖机(SaleMachine)： @interface SaleMachine : NSObject<NoMoneyDelegate,HasMoneyDelegate,SoldOutDelegate,SoldDelegate> @property (strong,nonatomic) NoMoneyState *noMoneyState; @property (strong,nonatomic) HasMoneyState *hasMoneyState; @property (strong,nonatomic) SoldOutState *soldOutState; @property (strong,nonatomic) SoldState *soldState; -(instancetype)initWithCount:(NSInteger)count; -(void)setCurrentState:(State *)currentState; -(void)putMoney; -(void)ejectMoney; -(void)pressButton; @end @interface SaleMachine() @property (strong,nonatomic) State *state; @property (assign,nonatomic) NSInteger productCount; @end @implementation SaleMachine -(instancetype)initWithCount:(NSInteger)count{ self=[super init]; if (self) { self.noMoneyState=[[NoMoneyState alloc]init]; self.noMoneyState.delegate=self; self.hasMoneyState=[[HasMoneyState alloc]init]; self.hasMoneyState.delegate=self; self.soldState=[[SoldState alloc]init]; self.soldState.delegate=self; self.soldOutState=[[SoldOutState alloc]init]; self.soldOutState.delegate=self; self.productCount=count; if (count) { self.state=self.noMoneyState; } } return self; } -(void)putMoney{ [self.state putMoney]; } -(void)ejectMoney{ [self.state ejectMoney]; } -(void)pressButton{ [self.state pressButton]; [self.state distribute]; } -(void)setCurrentState:(State *)currentState{ self.state=currentState; } #pragma mark - NoMoenyDelegate -(State *)geHasMoneyState{ return self.hasMoneyState; } #pragma mark - HasMoneyDelegate -(State *)getNoMoneyState{ return self.noMoneyState; } -(State *)getSoldState{ return self.soldState; } #pragma mark - SoldDelegate -(void)realseProduct{ NSLog(@"SoldDelegate-realseProduct:商品售出"); if (self.productCount) { self.productCount-=1; } } -(State *)getSoldOutState{ return self.soldOutState; } -(NSInteger)getCurrentCount{ return self.productCount; } @end 测试: SaleMachine *machine=[[SaleMachine alloc]initWithCount:1]; [machine putMoney]; [machine ejectMoney]; [machine putMoney]; [machine pressButton]; SaleMachine *next=[[SaleMachine alloc]initWithCount:1]; [next putMoney]; [next ejectMoney]; 测试效果: 状态模式的优缺点: 优点:状态模式允许一个对象基于内部状态有不同的行为，将行为委托给状态对象执行，状态转化可以由Context也可以由状态行为控制，比较灵活； 缺点:状态模式的使用必然会增加系统类和对象的个数。状态模式的结构与实现都较为复杂，如果使用不当将导致程序结构和代码的混乱。 本文转自Fly_Elephant博客园博客，原文链接：http://www.cnblogs.com/xiaofeixiang/p/5135479.html，如需转载请自行联系原作者
