javascript - 我可以从外部组件使用 useReducer

Question

现在我尝试使用 useReducer 创建一种管理状态和功能的新方法，但现在发现问题是“Hooks 只能在函数组件的主体内部调用” 有什么办法可以解决这个问题吗？

// App Component
import React from "react";

import { product, productDis } from "./ProductReducer";
//{product} is state,  {productDis} is dispatch

import { total } from "./TotalReducer";
//{total} is state and i dont need {totalDis}


const App = () => {
  return (
    <div>
      <button onClick={()=>productDis({type:'add',payload:'pen'})}>add</button>
      {product} {total}
    </div>
  );
};
export default App;

// ProductReducer Component
import React, { useReducer } from 'react';
import {totalDis} from './TotalReducer'
//{totalDis} is dispatch and i dont need {total}


export const [product, productDis] = useReducer((state, action) => {
    switch (action.type) {
        case "add": {
            const product_0 = 'pencil'
            const product_1 = `${action.payload} and ${product_0}`
            totalDis({
                type:'total_add',
                payload:'250'
            })
            return product_1;
        }
        default:
            return state;
    }
}, []);

// TotalReducer Component
import React, { useReducer } from 'react';

export const [total, totalDis] = useReducer((total, action) => {
    switch (action.type) {
        case "total_add": {
            const vat = action.payload*1.15
            return vat;
        }
        default:
            return total;
    }
}, 0)

当我单击显示屏上的按钮时，应该显示...“钢笔和铅笔 287.5”

但它显示“Hooks 只能在函数组件的主体内部调用”

有什么办法可以解决这个问题吗？或者我应该回归自然？

Answer 1

React hooks 只能在功能组件内部调用。钩子(Hook)状态是按组件实例维护的。如果必须重用钩子(Hook)，可以将它们提取到自定义钩子(Hook)中，这些钩子(Hook)是调用内置钩子(Hook)的函数，并且应该在功能组件内部调用:

export const useTotal = () => {
  const [total, totalDis] = useReducer((total, action) => {...}, 0);
  ...
  return [total, totalDis];
};

如果需要维护多个组件的公共(public)状态，则应将其维护在公共(public)父组件中并通过 props 提供给子组件:

const Root = () => (
  const [total, totalDispatcher] = useTotal();

  return <App {...{total, totalDispatcher}}/>
);

const App = props => {
  return (
    <div>{props.total}</div>
  );
};

或者上下文API:

const TotalContext = createContext();

const Root = () => (
  <TotalContext.Provider value={useTotal()}>
    <App/>
  </TotalContext.Provider>
);

const App = () => {
  const [total] = useContext(TotalContext);
  return (
    <div>{total}</div>
  );
};