状态没有反映在箭头函数中？

Question

Arrow functions上发布的类似问题只能访问由 useReducer 创建的初始状态，不能访问更新状态但不能解决。状态 (useReducer) 未反映在箭头函数中。一个简单的例子：React 组件const Component = ({ children }: Props) => {    const [state, dispatch] = useReducer(reducer, {visitor: false}) useEffect(() => {    someObject = new Connection({    onMessage: msg    onSuccess: () => dispatch({type: "Visitor", value: true})    })    return () => console.log("UNMOUNTING ");  }, []);    const msg = (request) => {        // visitor: false        console.log(state) // expected updated state, but instead see initial state, why?        // ... do more things    }    // visitor: true    console.log(state) // updated state is present here    return (        <Component.Provider value={{ state }}>            {children}        </Component.Provider>    )}减速机功能：const reducer = (state, action) => {    switch (action.type) {        case 'Visitor':          return {...state, visitor: true}        default:          return state    }}

Answer 1

您正在将回调传递给useEffect组件安装，此回调在value上有一个闭包。state{visitor: false}

// Closure on `state = {visitor: false}` passed to useEffect

useEffect(() => {

  msg();

}, [])