Redux-React 代码原理分析

Posted 2020-11-16

目标

react使用redux的主要目的是：
1）实现简洁统一的状态维护，提高代码可维护性；
2）实现简洁的注入依赖，避免重重传递参数；
Plug Any Data Into Any Component. This is the problem that Redux solves. It gives components direct access to the data they need.
3）实现自动化渲染。

index.js

应用的入口代码

import React from ‘react‘;
import { render } from ‘react-dom‘;
import Counter from ‘./Counter‘;
import { Provider } from ‘react-redux‘;
import { createStore } from ‘redux‘;

const initialState = {
  count: 0
};

function reducer(state = initialState, action) {
  switch(action.type) {
    case ‘INCREMENT‘:
      return {
        count: state.count + 1
      };
    case ‘DECREMENT‘:
      return {
        count: state.count - 1
      };
    default:
      return state;
  }
}

/**
* 1） 创建全局存储对象 store,传入合适的reducer.
*/
const store = createStore(reducer);

/**
* 2） 将store实例绑定到 App
*/

const App = () => (
  <Provider store={store}>
    <Counter/>
  </Provider>
);

render(<App />, document.getElementById(‘root‘));

组件代码

import React from ‘react‘;
import { connect } from ‘react-redux‘;

/**
* index.js创建的store全局对象，会注入到所有下级对象中，因此这里才可以使用dispatch函数来改变属性。
*/
class Counter extends React.Component {
  increment = () => {
    //实际上是调用全局store对象的dispatch函数
    this.props.dispatch({ type: ‘INCREMENT‘ });
  }

  decrement = () => {
    this.props.dispatch({ type: ‘DECREMENT‘ });
  }

  render() {
    return (
      <div>
        <h2>Counter</h2>
        <div>
          <button onClick={this.decrement}>-</button>
          <span>{this.props.count}</span>
          <button onClick={this.increment}>+</button>
        </div>
      </div>
    )
  }
}

//具体的属性转换函数
function mapStateToProps(state) {
  return {
    count: state.count
  };
}

//通过connect方法将store的state属性转换成本组件的属性
export default connect(mapStateToProps)(Counter);