javascript - 在上下文使用者上使用 useContext() 时反应上下文“属性‘状态’不存在”

Question

我正在尝试在我的 React 项目中实现上下文。每次我尝试实现这个上下文时，我都会得到同样的错误：

Property 'state' does not exist on type '{ count: number; currentColor: string; }'.

  > 40 |   let { state, dispatch } = React.useContext(ContextOne);
       |         ^

上下文提供程序代码：

import * as React from "react";

let ContextOne = React.createContext(initialState);

let initialState = {
  count: 10,
  currentColor: "#bada55"
};

let reducer = (state, action) => {
  switch (action.type) {
    case "reset":
      return initialState;
    case "increment":
      return { ...state, count: state.count + 1 };
    case "decrement":
      return { ...state, count: state.count - 1 };
    case "set-color":
      return { ...state, currentColor: action.payload };
  }
};

function ContextOneProvider(props) {
  let [state, dispatch] = React.useReducer(reducer, initialState);
  let value = { state, dispatch };


  return (
    <ContextOne.Provider value={value}>{props.children}</ContextOne.Provider>
  );
}

let ContextOneConsumer = ContextOne.Consumer;

export { ContextOne, ContextOneProvider, ContextOneConsumer };

我尝试了许多在线示例上下文提供程序，但每次调用 useContext() 时，都会出现相同的错误。需要修改哪些内容才能使 Context 正常工作？

- - - - - - - - - - - - - - - - - - - - - 编辑 - - - - ----------------------------------

感谢 soywood，这里是工作上下文提供程序代码：

import * as React from "react";

type State = {
  count: number
  currentColor: string
}

const initialState: State = {
  count: 10,
  currentColor: "#bada55",
};

type Context = {
  state: State
  dispatch: React.Dispatch<Action>
}

type Action = {
  type: string,
  payload: string
}
const ContextOne = React.createContext<Context>({
  state: initialState,
  dispatch: () => {},
});

// You need to define the type Action
const reducer: React.Reducer<State, Action> = (state, action) => {
  switch (action.type) {
    case "reset":
      return initialState;
    case "increment":
      return { ...state, count: state.count + 1 };
    case "decrement":
      return { ...state, count: state.count - 1 };
    case "set-color":
      return { ...state, currentColor: action.payload };
  }
};

function ContextOneProvider(props) {
  const [state, dispatch] = React.useReducer(reducer, initialState);
  const value: Context = { state, dispatch };

  return (
    <ContextOne.Provider value={value}>{props.children} </ContextOne.Provider>
  );
}

let ContextOneConsumer = ContextOne.Consumer;

export { ContextOne, ContextOneProvider, ContextOneConsumer };

标签： javascriptreactjsreact-nativereact-hooksreact-context

Answer 1

createContext参数类型应与您的值ContextOne.Provider类型匹配。您还需要改进您的类型以指导更多的TypeScript编译器：

import * as React from "react";

type State = {
  count: number
  currentColor: string
}

const initialState: State = {
  count: 10,
  currentColor: "#bada55",
};

type Context = {
  state: State
  dispatch: React.Dispatch<State>
}

const ContextOne = React.createContext<Context>({
  state: initialState,
  dispatch: () => {},
});

// You need to define the type Action
const reducer: React.Reducer<State, Action> = (state, action) => {
  switch (action.type) {
    case "reset":
      return initialState;
    case "increment":
      return { ...state, count: state.count + 1 };
    case "decrement":
      return { ...state, count: state.count - 1 };
    case "set-color":
      return { ...state, currentColor: action.payload };
  }
};

function ContextOneProvider(props) {
  const [state, dispatch] = React.useReducer(reducer, initialState);
  const value: Context = { state, dispatch };

  return (
    <ContextOne.Provider value={value}>{props.children} </ContextOne.Provider>
  );
}

let ContextOneConsumer = ContextOne.Consumer;

export { ContextOne, ContextOneProvider, ContextOneConsumer };