有限状态机FSM

一、什么是有限状态机

有限状态机简写为FSM（Finite State Machine），它有4个要素，即现态、条件、动作、次态。“现态”和“条件”是因，“动作”和“次态”是果。

现态：是指当前所处的状态。
条件：又称为“事件”，当一个条件被满足，将会触发一个动作，或者执行一次状态的迁移。
动作：条件满足后执行的动作。动作执行完毕后，可以迁移到新的状态，也可以仍旧保持原状态。动作不是必需的，当条件满足后，也可以不执行任何动作，直接迁移到新状态。
次态：条件满足后要迁往的新状态。“次态”是相对于“现态”而言的，“次态”一旦被激活，就转变成新的“现态”了。

二、Flutter中的Bloc

触发事件 —> bloc派发event —> bloc中map根据不同的event执行不同逻辑 —> 生成新的状态state —> 页面根据新的状态重新渲染

三、Redux

Store 就是保存数据的地方，你可以把它看成一个容器。整个应用只能有一个 Store。
State 的变化，会导致 View 的变化。但是，用户接触不到 State，只能接触到 View。所以，State 的变化必须是 View 导致的。
Action 就是 View 发出的通知，表示 State 应该要发生变化了。store.dispatch()是 View 发出 Action 的唯一方法。
Store 收到 Action 以后，必须给出一个新的 State，这样 View 才会发生变化。这种 State 的计算过程就叫做 Reducer。
Reducer 是一个函数，它接受 Action 和当前 State 作为参数，返回一个新的 State。
Reducer 函数最重要的特征是，它是一个纯函数。也就是说，只要是同样的输入，必定得到同样的输出。

四、iOS中实现一个FSM( TransitionKit)

三方库：TransitionKit

1.State

每个状态有四个闭包，可以在创建State的时候传入action

WillExit
WillEnter
DidExit
DidEnter

2.Event

每个Event代表从某个状态（sourceStates）变化到另一个状态（destinationState）

sourceStates是一个数组，可以变到destinationState的State都可以放在数组中
event有WillFire和DidFire闭包，以传入action

3.Transition

用来运输State变化过程中的各个对象，包括：

event
sourceState
destinationState
stateMachine
userInfo （扩展参数，在Machine触发event的时候传入）

4.Machine

FSM控制中心

1. 持有所有States
1. 持有所有Event
1. 需要赋予一个初始的state
1. 调用activate启动Machine
1. 调用fireEvent触发状态的切换，触发过程会分别调用state和event的闭包实现action，并且会发送一个通知

5.例子

 	// 1.核心machine
    TKStateMachine *machine = [[TKStateMachine alloc] init];
    
    // 2.定义未读状态
    TKState *unread = [TKState stateWithName:@"unread"];
    
    [unread setWillExitStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"unread WillExit: %@", userInfo);
    }];
    
    [unread setWillEnterStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"unread WillEnter: %@", userInfo);
    }];
    
    [unread setDidExitStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"unread DidExit: %@", userInfo);
    }];
    
    [unread setDidEnterStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"unread DidEnter: %@", userInfo);
    }];
    
    // 3.定义已读状态
    TKState *read = [TKState stateWithName:@"read"];
    
    [read setWillExitStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"read WillExit: %@", userInfo);
    }];
    
    [read setWillEnterStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"read WillEnter: %@", userInfo);
    }];
    
    [read setDidExitStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"read DidExit: %@", userInfo);
    }];
    
    [read setDidEnterStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"read DidEnter: %@", userInfo);
    }];
    
    // 4.定义删除状态
    TKState *delete = [TKState stateWithName:@"delete"];
    
    [delete setWillExitStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"delete WillExit: %@", userInfo);
    }];
    
    [delete setWillEnterStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"delete WillEnter: %@", userInfo);
    }];
    
    [delete setDidExitStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"delete DidExit: %@", userInfo);
    }];
    
    [delete setDidEnterStateBlock:^(TKState *state, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"delete DidEnter: %@", userInfo);
    }];
    
    TKEvent *readEvent = [TKEvent eventWithName:@"read" transitioningFromStates:@[unread] toState:read];
    
    [readEvent setWillFireEventBlock:^(TKEvent *event, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"readEvent WillFire: %@", userInfo);
    }];
    
    [readEvent setDidFireEventBlock:^(TKEvent *event, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"readEvent DidFire: %@", userInfo);
    }];
    
    TKEvent *deleteEvent = [TKEvent eventWithName:@"delete" transitioningFromStates:@[read, unread] toState:delete];
    
    [deleteEvent setWillFireEventBlock:^(TKEvent *event, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"deleteEvent WillFire: %@", userInfo);
    }];
    
    [deleteEvent setDidFireEventBlock:^(TKEvent *event, TKTransition *transition) {
        NSString *userInfo = transition.userInfo[@"key"];
        NSLog(@"deleteEvent DidFire: %@", userInfo);
    }];
    
    // 5.配置并启动machine
    
    NSLog(@"🔥1.初始化machine");
    
    [machine addStates:@[read, unread, delete]];
    [machine addEvents:@[readEvent, deleteEvent]];
    [machine setInitialState:unread];
    [machine activate];
    
    // 6.触发event
    
    NSError *error = nil;
    
    NSLog(@"-------->1.当前状态---> %@", [machine currentState]);
    
		// 触发从unread到read的event
    [machine fireEvent:readEvent userInfo:@{@"key": @"unread to read"} error:&error];
    
    NSLog(@"-------->2.当前状态---> %@", [machine currentState]);
    
		// 触发从unread/delete
    [machine fireEvent:deleteEvent userInfo:@{@"key": @"unread/read to delete"} error:&error];
    
    NSLog(@"-------->3.当前状态---> %@", [machine currentState]);

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