我的第一个 react redux demo

最近学习react redux，先前看过了几本书和一些博客之类的，感觉还不错，比如《深入浅出react和redux》,《React全栈++Redux+Flux+webpack+Babel整合开发》，《React与Redux开发实例精解》， 个人觉得《深入浅出react和redux》这本说讲的面比较全， 但是 很多都是蜻蜓点水， 不怎么深入。这里简单记录一个redux 的demo， 主要方便以后自己查看，首先运行界面如下：

项目结构如下：

这里我们一共有2个组件，都在components文件夹下面，Picker.js实现如下：

import React from 'react';
import PropTypes from 'prop-types';
function Picker({value, onChange, options}) {
    return(
        <span>
            <h1>{value}</h1>
            <select onChange={e=>onChange(e.target.value)} value={value}>
                {options.map(o=>
                    <option value={o} key={o}>{o}</option>
                    )}
            </select>
        </span>
    );
}

Picker.propTypes = {
    options:PropTypes.arrayOf(PropTypes.string.isRequired).isRequired,
    value:PropTypes.string.isRequired,
    onChange:PropTypes.func.isRequired,
};

export default Picker;这里的onChange事件是传递进来的，最终就是要触发一个action，Posts.js的实现如下：

import React from 'react';
import PropTypes from 'prop-types';
function Posts ({posts}){
    return(
        <ul>
            {
                posts.map((p,i)=>
                    <li key={i}>{p.title}</li>
                )
            }
        </ul>
    );
}

Posts.propTypes = {
    posts:PropTypes.array.isRequired,
};

export default Posts;

1. 现在来看看actions/index.js的实现：

import fetch from 'isomorphic-fetch';

export const REQUEST_POSTS = 'REQUEST_POSTS';
export const RECEIVE_POSTS = 'RECEIVE_POSTS';
export const SELECT_REDDIT = 'SELECT_REDDIT';
export const INVALIDATE_REDDIT = 'INVALIDATE_REDDIT';

export function selectReddit(reddit){
    return{
        type:SELECT_REDDIT,
        reddit,
    };
}

export function invalidateReddit(reddit){
    return {
        type:INVALIDATE_REDDIT,
        reddit,
    };
}

export function requestPosts(reddit){
    return {
        type:REQUEST_POSTS,
        reddit,
    };
}

export function receivePosts(reddit,json){
    return{
        type:RECEIVE_POSTS,
        reddit,
        posts:json.data.children.map(x=>x.data),
        receivedAt:Date.now(),
    };
}

function fetchPosts(reddit){
    return dispatch=>{
        dispatch(requestPosts);
        return fetch(`https://www.reddit.com/r/${reddit}.json`)
        .then(r=>r.json())
        .then(j=>dispatch(receivePosts(reddit,j)));
    }
}

function shouldFetchPosts(state,reddit){
    const posts = state.postsByReddit[reddit];
    if(!posts){
        return true;
    }
    if(posts.isFetching){
        return false;
    }
    return posts.didInvalidate;
}

export function fetchPostsIfNeeded(reddit){
    return (dispatch,getState)=>{
        if(shouldFetchPosts(getState(),reddit)){
            return dispatch(fetchPosts(reddit));
        }
        return null;
    };
}

主要是暴露出selectReddit，invalidateReddit，requestPosts，receivePosts和fetchPostsIfNeeded几个action，而fetchPostsIfNeeded才是主要的，首先调用shouldFetchPosts方法来检查是否需要获取数据， 如果是的话就调用fetchPosts方法，而fetchPosts方法返回的是一个function，这里我的项目使用了redux-thunk， 看看redux-thunk的实现如下：

function createThunkMiddleware(extraArgument) {
  return ({ dispatch, getState }) => next => action => {
    if (typeof action === 'function') {
      return action(dispatch, getState, extraArgument);
    }

    return next(action);
  };
}

const thunk = createThunkMiddleware();
thunk.withExtraArgument = createThunkMiddleware;

export default thunk;

所以在fetchPostsIfNeeded中的dispatch(fetchPosts(reddit)) 最终会进入到redux-thunk里面，fetchPosts(reddit)返回的是一个function如下，所以这里会进入这个action里面，也就是 return action(dispatch, getState, extraArgument);

function fetchPosts(reddit){
    return dispatch=>{
        dispatch(requestPosts);
        return fetch(`https://www.reddit.com/r/${reddit}.json`)
        .then(r=>r.json())
        .then(j=>dispatch(receivePosts(reddit,j)));
    }
}

所以在fetchPosts里面的dispatch参数就是redux-thunk里面return action(dispatch, getState, extraArgument) 的dispatch。

在这里的function里面， 一般发起http请求前有一个 状态改变（dispatch(requestPosts);）， http请求成功后有一个 状态改变（dispatch(receivePosts(reddit,j))），失败也会有状态改变（这里忽律失败的case）

接下来看看containers\App.js

import React, { Component } from 'react';
import PropTypes from 'prop-types';
import { connect } from 'react-redux';
import { selectReddit, fetchPostsIfNeeded, invalidateReddit } from '../actions';
import Picker from '../components/Picker';
import Posts from '../components/Posts';

class App extends Component{
    constructor(props){
        super(props);
        this.handleChange=this.handleChange.bind(this);
        this.handleRefreshClick=this.handleRefreshClick.bind(this);
    }

    componentDidMount(){
        console.log('执行componentDidMount');
        const { dispatch, selectedReddit } = this.props;
        dispatch(fetchPostsIfNeeded(selectedReddit));
    }

    componentWillReceiveProps(nextProps){
        console.log('执行componentWillReceiveProps', nextProps);
        if(nextProps.selectedReddit !==this.props.selectedReddit)
        {
            const { dispatch, selectedReddit } = this.props;
            dispatch(fetchPostsIfNeeded(selectedReddit));
        }
    }

    handleChange(nextReddit){
        this.props.dispatch(selectReddit(nextReddit));
    }

    handleRefreshClick(e){
        e.preventDefault();
        const {dispatch, selectedReddit } = this.props;
        dispatch(invalidateReddit(selectedReddit));
        dispatch(fetchPostsIfNeeded(selectedReddit));
    }

    render(){
        const { selectedReddit, posts, isFetching, lastUpdated } = this.props;
        const isEmpty = posts.length === ;
        const message = isFetching ? <h2>Loading...</h2> : <h2>Empty.</h2>;
        return(
            <div>
                <Picker value={selectedReddit} onChange={this.handleChange} options={['reactjs', 'frontend']} />
                <p>
                    { lastUpdated && <span>Last updated at {new Date(lastUpdated).toLocaleDateString()}.</span>}
                    {!isFetching && <a href="#" onClick={this.handleRefreshClick}>Refresh</a>}
                </p>
                {isEmpty?message:<div style={{opacity:isFetching?0.5:}}><Posts posts={posts}/></div>}
            </div>
        );
    }
}
App.propTypes = {
    selectedReddit:PropTypes.string.isRequired,
    posts:PropTypes.array.isRequired,
    isFetching:PropTypes.bool.isRequired,
    lastUpdated:PropTypes.number,
    dispatch:PropTypes.func.isRequired
};

function mapStateToProps(state){
    const { selectedReddit, postsByReddit } = state;
    const { isFetching, lastUpdated, items: posts,} = postsByReddit[selectedReddit] || { isFetching: true, items: [], };
    return {
        selectedReddit,
        posts,
        isFetching,
        lastUpdated,
    };
}
export default connect(mapStateToProps)(App);

只是要注意一下componentDidMount方法里面是调用dispatch(fetchPostsIfNeeded(selectedReddit));的，页面加载后就发送默认的http请求。

在来看看reducers\index.js:

import {combineReducers} from 'redux';
import {SELECT_REDDIT,INVALIDATE_REDDIT,REQUEST_POSTS,RECEIVE_POSTS} from '../actions';

function selectedReddit (state='reactjs',action) {
    switch(action.type){
        case SELECT_REDDIT:
            return action.reddit;
        default:
        return state === undefined ? "" : state;
    }
}

function posts(state= { isFetching: false, didInvalidate: false,items: [],}, action){
    switch(action.type){
        case INVALIDATE_REDDIT:
            return Object.assign({},state,{didInvalidate:true});
        case REQUEST_POSTS:
            return Object.assign({},state,{isFetching:true,didInvalidate:false});
        case RECEIVE_POSTS:
            return Object.assign({},state,{isFetching:false,didInvalidate:false,items:action.posts,lastUpdated:action.receivedAt});
        default:
            return state;
    }
}

function postsByReddit(state={},action){
    switch(action.type){
        case INVALIDATE_REDDIT:
        case RECEIVE_POSTS:
        case REQUEST_POSTS:
            return Object.assign({},state,{[action.reddit]:posts(state[action.reddit],action)});
        default:
            return state === undefined ? {} : state;
    }
}

const rootReducer =combineReducers({postsByReddit,selectedReddit});
export default rootReducer;

这里用combineReducers来合并了postsByReddit和selectedReddit两个Reducers，所以每个action都会进入这2个Reducers（也不知道我的理解是否正确），比如action type 是INVALIDATE_REDDIT，selectedReddit 什么都不处理，直接返回state，然而postsByReddit会返回我们需要的state。 还有就是经过combineReducers合并后的数据，原先postsByReddit需要的state现在就只能通过state.postsByReddit来获取了。

还有大家主要到了没有， 这里有return state === undefined ? "" : state; 这样的写法， 那是combineReducers在初始化的时候会传递undefined ，combineReducers->assertReducerShape的实现如下：

所以默认的state传递的是undefined，而我们的reducer也是没有处理ActionTypes.INIT的

现在来看看store/configureStore.js

import {createStore,applyMiddleware,compose} from 'redux';
import thunkMiddleware from 'redux-thunk';
import  logger from 'redux-logger';
import rootReducer from '../reducers';

const store=createStore(rootReducer,initialState,compose(
        applyMiddleware(thunkMiddleware,logger),
        window.devToolsExtension? window.devToolsExtension():f=>f
    ));
    if(module.hot){
        module.hot.accept('../reducers',()=>{
            const nextRootReducer=require('../reducers').default;
            store.replaceReducer(nextRootReducer);
        });
    }
    return store;
}

module.hot实在启用了热跟新后才可以访问的。

index.js实现：

import 'babel-polyfill';
import React from 'react';
import {render} from 'react-dom';
import {Provider} from 'react-redux';
import App from './containers/App';
import configureStore from './store/configureStore';

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

server.js实现：

var webpack = require('webpack');
var webpackDevMiddleware = require('webpack-dev-middleware');
var webpackHotMiddleware = require('webpack-hot-middleware');
var config = require('./webpack.config');

var app= new (require('express'))();
var port= ;

var compiler = webpack(config);
app.use(webpackDevMiddleware(compiler, {noInfo:true, publicPath:config.output.publicPath}));
app.use(webpackHotMiddleware(compiler));

app.get("/",function(req,res){
    res.sendFile(__dirname+'/index.html');
});

app.listen(port,function(error){
    if(error){
        console.error(error);
    }
    else{
        console.info("==>