Take about Redux I

Huiqiang Jiang2018年04月23日 21:23:43文章访问量:

本来我们组用的前端技术一般也就是利用基于react的AntD脚手架后来组里来了一个pku的dalao 科普了 react全家桶

目前我们项目里除了基础的redux之外，还用了saga中间件 react-router

在了解redux之前可能你不一定要用redux 经常有人会说不会redux说明你不需要用redux“You Might Not Need Redux” ————————————————————————

什么是Redux？

讲起来redux第一次代码提交也就在三年前一晃作为react家族一员被广泛应用于各web构建

先来看一段官方文档的介绍 Redux 是 JavaScript 状态容器，提供可预测化的状态管理。

通俗的来讲redux做的工作类似于state做的工作，它是来管理数据状态的，解决数据变化和异步这两个问题的工具。将原来事件驱动的服务，变化为数据驱动的服务。

redux有什么特点？

redux一般是由

action
reducer
store
MiddleWare

相对于state，首先redux里面的数据是可以跨页面的，其次redux的数据是只读的，如果需要更改数据必须调用相应的action。当然这点也很好理解，因为redux读取时用的是this.props props本身就是只读的。（从这个角度也可以把redux理解为父组件统一管理状态的库） reducer函数是一个纯函数，只根据对应的action和之前的state，返回新的state。

Action 顾名思义是一个存放行为的函数。组件通过dispath调用action函数，action函数收到request 把对应的type 和相应的参数传递给 store

import types from '../constants/actionTypes';
import { createActions } from '../util/utils';

//同步action
export function fetchCollapseChange(collapse) {
  return {
    type: types.CHANGE_COLLAPSE,
    payload: {
      collapse,
    },
  };
}

//异步action
export const fetchTimeInfo = createActions([
  types.FETCH_TIME_INFO_REQUEST,
  types.FETCH_TIME_INFO_SUCCESS,
  types.FETCH_TIME_INFO_FAILURE,
]);

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import { createConstants } from '../util/utils';

export default createConstants(

  'CHANGE_COLLAPSE',

  'FETCH_TIME_INFO_REQUEST',
  'FETCH_TIME_INFO_SUCCESS',
  'FETCH_TIME_INFO_FAILURE',
}

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const LoadStatus = {
  CACHED: 'cached',
  CHECKING: 'checking',
  LOADING: 'loading',
  UPDATING: 'updating',
  PROCESSING: 'processing',
  FINISHED: 'finished',
  ERROR: 'error',
  NONE: 'none',
};

export default LoadStatus;

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Reducer 当Action 执行之后得到了对应的Action_type。根据这些type，reducer函数更新相应的数据，注意reducer是一个纯函数，不执行复杂的数据处理过程。 Reducer 分为初始化，action更新两部分。

import types from '../constants/actionTypes';
import LoadStatus from '../constants/loadStatus';

function getInitState() {
  return {
    loginLayout: {
      collapse: false,
      time: '0000-00-00 00:00',
      timeNum: 0,
      loadStatus: LoadStatus.NONE,
    },
  };
}

function layoutReducer(state = getInitState(), action) {
  const { payload } = action;
  switch (action.type) {
    case types.CHANGE_COLLAPSE:
      return {
        ...state,
        loginLayout: {
          ...state.loginLayout,
          collapse: payload.collapse,
        },
      };
    case types.FETCH_TIME_INFO_REQUEST:
      return {
        ...state,
        loginLayout: {
          ...state.loginLayout,
          loadStatus: LoadStatus.LOADING,
        },
      };
    case types.FETCH_TIME_INFO_SUCCESS:
      return {
        ...state,
        loginLayout: {
          ...state.loginLayout,
          loadStatus: LoadStatus.FINISHED,
          time: payload.time,
          timeNum: payload.result,
        },
      };
    case types.FETCH_TIME_INFO_FAILURE:
      return {
        ...state,
        loginLayout: {
          ...state.loginLayout,
          loadStatus: LoadStatus.ERROR,
        },
      };
    default:
      return state;
  }
}

export default layoutReducer;

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import { combineReducers } from 'redux';
import { routerReducer } from 'react-router-redux';
import layoutReducer from './layoutReducer';

const rootReducer = combineReducers({
  layout: layoutReducer,
});

export default rootReducer;

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Storestore就相当于一个存储库，受到各种函数调用，当store里面的参数值更新之后把更新后的参数返回给各个组件。

import { connect } from 'react-redux';
import { withRouter } from 'react-router-dom';
import { fetchUserInfo } from './actions/userAction';
import { fetchCollapseChange } from './actions/layoutAction';

//把所有state值 存入props中
function mapStateToProps(state) {
  const {
    user: {
      loginUser: {
        isAdmin,
      },
    },
    layout: {
      loginLayout: {
        collapse,
      },
    },

  } = state;
  return {
    isAdmin,
    collapse,
  };
}

//把所有dispatch 函数 存入props
function mapDispatchToProps(dispatch) {
  return {
    fetchUserInfo() {
      dispatch(fetchUserInfo.request());
    },
    fetchCollapseChange(collapse) {
      dispatch(fetchCollapseChange(collapse));
    },
  };
}

//withRouter
export default withRouter(connect(
  mapStateToProps,
  mapDispatchToProps,
)(AppLayout));

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当props更新之后 render会重新渲染一次以实现类似setState的功能。此外redux可以通过componentWillReceiveProps 获取下一次props值根据此值可以做相应的操作

  componentWillReceiveProps(nextProps) {
    const {
      loadStatus: nextLoadStatus,
    } = nextProps;

    const {
      loadStatus,
    } = this.props;

    const { filterVis, filtered } = this.state;
    if (loadStatus === LoadStatus.LOADING && nextLoadStatus === LoadStatus.FINISHED && filterVis) {
      this.onChangeSearch(filtered);
    }
  }

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Sagasaga是实现异步Redux的一个中间件负责传递ajax请求和根据进度返回相应的loadStatus 、相应的返回值

import baseApi from './baseApi';

export default {
  fetchTimeInfo() {
    return baseApi.get('/system/time');
  },
};

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import axios from 'axios';
import { backendUrl } from '../util/constant';

const baseApi = axios.create({
  baseURL: backendUrl,
  timeout: 30000,
  withCredentials: true,
  changeOrigin: true,
});

baseApi.interceptors.response.use((response) => {
  const { data } = response;
  if (typeof data.success === 'boolean' && !data.success) {
    return Promise.reject(response);
  }
  return {
    result: data,
    receivedAt: Date.now(),
    response,
  };
}, (err) => {
  console.log(err);
  if (err.response.status === 302) {
    location.href = backendUrl;
    window.localStorage.setItem('last', window.location.href);
    console.log(`set last to ${window.location.href}`);
  }
  return Promise.reject(err);
});

export default baseApi;

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import { call, put, takeLatest } from 'redux-saga/effects';
import types from '../constants/actionTypes';
import layoutApi from '../apis/layoutApi';
import { fetchTimeInfo } from '../actions/layoutAction';
import { timeStamp2String } from '../util/constant';

export function* fetchTimeInfoTask() {
  try {
    const payload = yield call(layoutApi.fetchTimeInfo);
    payload.time = timeStamp2String(payload.result);
    yield put(fetchTimeInfo.success(payload));
  } catch (err) {
    yield put(fetchTimeInfo.failure(err));
  }
}

export default function* layoutSaga() {
  yield takeLatest(types.FETCH_TIME_INFO_REQUEST, fetchTimeInfoTask);

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import { all } from 'redux-saga/effects';
import layoutSaga from './layoutSaga';

export default function* rootSaga() {
  yield all([
    layoutSaga(),
  ]);
}

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import { applyMiddleware, createStore, compose } from 'redux';
import createSagaMiddleware from 'redux-saga';
import thunkMiddleware from 'redux-thunk';
import rootReducer from '../reducers';
import rootSaga from '../sagas';
import DevTools from '../containers/DevTools';

export default function configureStore(initialState) {
  const sagaMiddleware = createSagaMiddleware();

  const middlewares = [
    thunkMiddleware,
    sagaMiddleware,
  ];

  console.log(`NODE_ENV: ${process.env.NODE_ENV}`);
  let store = {};
  if (process.env.NODE_ENV === 'production') {
    store = createStore(rootReducer, initialState, compose(applyMiddleware(...middlewares)));
  } else {
    store = createStore(rootReducer, initialState, compose(
      applyMiddleware(...middlewares),
      DevTools.instrument(),
    ));
  }

  sagaMiddleware.run(rootSaga);

  return store;
}

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Saga 可以实现ajax请求统一管理通过loadStatus来判断api调用状态通过选择takeLeading/takeLatest/takeEvery 来管理ajax请求避免堆积pending

数据流redux的生命周期从调用dispatch开始当组件开始渲染调用了某个action 函数可能是写在componentDidMount 亦或是普通函数中的 this.props.xxxx(); 之后调用mapDispatchToProps 通过withRouter传递给action函数 action拿到请求之后返回相应的type 之后reducer执行相应的更新store

相对而言异步调用action会分两步走一开始的type 是XXXX.REQUESTaction之后调用一次reducer 之后执行一次api 当收到返回值之后调用saga函数 saga函数会自动返回一个type XXXX.SUCCESS 如果超时未收到返回则 action 返回 type XXXX.FAILURED 之后第二次reducer

此外Rudux 自带非常友好的调试机制通过contr + q 调用 contr + h切换 ———————————————————————— PS：参考：

updated 4/23/2018

You can use this BibTex to reference this blog if you find it useful and want to quote it.

Redux JavaScript React