react-redux

主要： react-redux与redux并不完全一样

1. 主要特征

• ui组件

用户提供的页面

• 容器组件
  由 React-Redux 自动生成

2. 使用方法

• TodoList 是Ul组件
• mapStateToProps 将state映射到 UI 组件的参数（props）
• mapDispatchToProps 将用户对 UI 组件的操作映射成 Action
• connect方法可以省略mapStateToProps参数，那样的话，UI 组件就不会订阅Store，就是说 Store 的更新不会引起 UI 组件的更新。

import { connect } from 'react-redux'

const VisibleTodoList = connect(
  mapStateToProps,
  mapDispatchToProps
)(TodoList)

3. mapStateToProps

• 建立一个从（外部的）state对象到（UI 组件的）props对象的映射关系。
  @params: state<Object> state对象
  @params: props<Object> 容器组件的props对象

const mapStateToProps = (state, ownProps) => {
  return {
    active: state.count
  }
}

4. mapDispatchToProps

• 接收一个回调函数
  拥有 dispatch， ownProps 两个参数

const mapDispatchToProps = (
  dispatch,
  ownProps
) => {
  return {
    onClick: () => {
      dispatch({
        type: 'SET_VISIBILITY_FILTER',
        filter: ownProps.filter
      });
    }
  };
}

• 接收一个对象

const mapDispatchToProps = {
  onClick: (filter) => {
    type: 'SET_VISIBILITY_FILTER',
    filter: filter
  };
}

5. <Provider> 组件

• React-Redux 提供Provider组件，可以让所有容器组件拿到state。

import { Provider } from 'react-redux'
import { createStore } from 'redux'
import todoApp from './reducers'
import App from './components/App'

let store = createStore(todoApp);

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

• store放在了上下文对象context上面。然后，子组件就可以从context拿到store

class VisibleTodoList extends Component {
  componentDidMount() {
    const { store } = this.context;
    this.unsubscribe = store.subscribe(() =>
      this.forceUpdate()
    );
  }

  render() {
    const props = this.props;
    const { store } = this.context;
    const state = store.getState();
    // ...
  }
}

VisibleTodoList.contextTypes = {
  store: React.PropTypes.object
}

6. 完整代码

import React, { Component } from 'react'
import PropTypes from 'prop-types'
import ReactDOM from 'react-dom'
import { createStore } from 'redux'
import { Provider, connect } from 'react-redux'

// React component
class Counter extends Component {
  render() {
    const { value, onIncreaseClick } = this.props
    return (
      <div>
        <span>{value}</span>
        <button onClick={onIncreaseClick}>Increase</button>
      </div>
    )
  }
}

Counter.propTypes = {
  value: PropTypes.number.isRequired,
  onIncreaseClick: PropTypes.func.isRequired
}

// Action
const increaseAction = { type: 'increase' }

// Reducer
function counter(state = { count: 0 }, action) {
  const count = state.count
  switch (action.type) {
    case 'increase':
      return { count: count + 1 }
    default:
      return state
  }
}

// Store
const store = createStore(counter)

// Map Redux state to component props
function mapStateToProps(state) {
  return {
    value: state.count
  }
}

// Map Redux actions to component props
function mapDispatchToProps(dispatch) {
  return {
    onIncreaseClick: () => dispatch(increaseAction)
  }
}

// Connected Component
const App = connect(
  mapStateToProps,
  mapDispatchToProps
)(Counter)

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