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。