创建上下文context

import React, { useReducer, createContext } from 'react';

import { Counter } from './context';

import { addCount, minusCount, reducer } from './reducers';

/**
 * {Provider,Consumer} = createContext(defaultValue)
 * defaultValue：只是初始化的值，
 * Provider：发布者，value接收的参数个数以及类型要和defaultValue一致
 * Consumer：订阅者
 */

/** 当前生成的上下文需要向外暴露给子组件使用 */
export const CountContext = createContext({ text: '', count: 0, count2: 0 });

export default function UseContext() {
  /** useReducer的第二个参数就是reducer函数接收的state */
  const [state, dispatch] = useReducer(reducer, { count: 0 });
  // 为了区分不同的useReducer
  const [state2, dispatch2] = useReducer(reducer, { num: 0 });
  const initState = 'useReducer+Context的使用'; // initState如果不是字符串，eslint会报错

  const providerValue = {
    text: initState, //普通参数
    count: state.count, //reducer参数
    count2: state2.num, //reducer参数
    count12: state2.num, //多余的参数无法接收，而且eslint会报错
  };

  return (
    <div>
      <br />
      <button onClick={() => addCount(dispatch)}>+1</button>

      <button onClick={() => minusCount(dispatch2)}>- 1</button>

      {/* Provider的value接收的值跟createContext的参数个数以及类型都要一致 */}
      <CountContext.Provider value={{ ...providerValue }}>
        <Counter></Counter>
      </CountContext.Provider>
    </div>
  );
}

useContext使用

import React, { useContext } from 'react';

import { CountContext } from './index';

export function Counter() {
  /** 利用useContext注入父组件的context上下文 */
  const { text, count, count2 } = useContext(CountContext);

  return <h2>{count + '=>' + text + '<=' + count2}</h2>;
}

reducer

import { ADD, MINUS, TIMES, DIVIDE } from './constant';


export const reducer = (state: any, action: any) => {
  switch (action.type) {
    case ADD:
      return {
        ...state,
        count: state.count + 1
      }
      break;
    case MINUS:
      return {
        ...state,
        num: state.num - 1
      }
      break;
    default:
      break;
  }
}

export const addCount = (dispatch: any) => {
  dispatch({
    type: ADD,
  });
}

export const minusCount = (dispatch: any) => {
  dispatch({
    type: MINUS,
  });
}