React Hook: useSelector + useDispatch 用法例子

当函数式组件要使用 redux store 时调用这两个钩子函数。如果是类组件要使用 redux，可以使用另一个函数 connect.

函数式组件使用 Redux

例子,首先建立 redux store. 一个App 只能有唯一个一个地个 redux store。
src/store/index.js，此文件是一个手动建立的文件，这样命名文件是 convention.

// src/store/index.js
import { createStore } from "redux";
const counterReducer = (state = { counter: 0 }, action) => {
  if (action.type === "increment") {
    return { counter: state.counter   1 };
  }
  if (action.type === "decrement") {
    return { counter: state.counter - 1 };
  }
  return state;
};

const store = createStore(counterReducer);
export default store;

然后在组件树顶层用 store 来 wrap 需要使用此store的组件。

// 组件树顶层 index.js
import React from "react";
import ReactDOM from "react-dom";
import { Provider } from "react-redux";

import "./index.css";
import App from "./App";
import store from "./store/index";

ReactDOM.render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById("root")
);

最后在需要使用 store 的组件中调用这两个钩子函数，useSelector 用来获取组件需要的state 数据。useDispatch 用来获取 dispatch 函数,

// src/components/counter.js
import { useSelector, useDispatch } from "react-redux";
import classes from "./Counter.module.css";

const Counter = () => {
  const dispatch = useDispatch();
  const counter = useSelector((state) => state.counter);

  const incrementHandler = () => {
    dispatch({ type: "increment" });
  };
  const decrementHandler = () => {
    dispatch({ type: "decrement" });
  };

  const toggleCounterHandler = () => {};

  return (
    <main className={classes.counter}>
      <h1>Redux Counter</h1>
      <div className={classes.value}>{counter}</div>
      <div>
        <button onClick={incrementHandler}>Increment</button>
        <button onClick={decrementHandler}>Decrement</button>
      </div>
      <button onClick={toggleCounterHandler}>Toggle Counter</button>
    </main>
  );
};
export default Counter;

浏览器截图，起始计数为0，点击 Increment 按钮加 1，点击Decrement 按钮减 1。

类组件使用 Redux

将上面的 src/components/counter.js 改成使用 class components：

import { Component } from "react";
import { connect } from "react-redux";
import classes from "./Counter.module.css";

class Counter extends Component {
  incrementHandler() {
    this.props.increment();
  }
  decrementHandler() {
    this.props.decrement();
  }
  toggleCounterHandler() {}

  render() {
    return (
      <main className={classes.counter}>
        <h1>Redux Counter</h1>
        <div className={classes.value}>{this.props.counter}</div>
        <div>
          <button onClick={this.incrementHandler.bind(this)}>Increment</button>
          <button onClick={this.decrementHandler.bind(this)}>Decrement</button>
        </div>
        <button onClick={this.toggleCounterHandler}>Toggle Counter</button>
      </main>
    );
  }
}

const mapStateToProps = (state) => {
  return {
    counter: state.counter,
  };
};

const mapDispatchToProps = (dispatch) => {
  return {
    increment: () => dispatch({ type: "increment" }),
    decrement: () => dispatch({ type: "decrement" }),
  };
};

export default connect(mapStateToProps, mapDispatchToProps)(Counter);

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