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redux简明学习

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前面的话

  这几天被redux折腾的够呛,看了很多视频,也看了很多资料。很多时候,感觉好像顿悟了,但实际上只是理解了其中的一个小概念而已。真正去做项目的时候,还是会卡壳。可能是学CSS和Javascript时花的时间太久了,学redux的时候有点浮躁。还有就是redux内容实在是不少,全部都看都理解,好像没什么必要。不看吧,用的时候总是有点力不从心。于是,决定把这些资料按自己的理解写成博客,方便自己回忆思路,也希望能帮助到需要的人

 

核心概念

  redux专注于状态管理,把所有的状态都存在一个对象中。核心概念包括:store、state、action、reducer

【store】

  store是保存数据的地方,redux提供createStore函数来生成 Store。函数参数是后面要介绍的reducer

import { createStore } from redux
const store = createStore(reducer)

【state】

  state是store的某个时刻的快照,可以通过store.getState()取得当前时刻的state

const state = store.getState()

【action】

  action用来改变state。action是一个对象,其中的type属性是必须的,其他的属性一般用来设置改变state需要的数据

const action = {
  type: ADD_ONE,
  num: 1
}

  store.dispatch()是发出action的唯一方法

const action = {
  type: ADD_ONE,
  num: 1
}
store.dispatch(action)

【reducer】

  reducer 是一个函数,它接受action和当前state作为参数,返回一个新的state

import { createStore } from redux
const store = createStore(reducer)
const reducer = (state = 10, action) => {
  switch (action.type) {
    case ADD_ONE:
      return state + action.num;
    default: 
      return state;
  }
};

  当store.dispatch发送过来一个新的action,store就会自动调用reducer,得到新的state

 

简单实例

  多余的概念不再介绍,下面用上面介绍的这四个核心概念实现一个简单的实例,将create-react-app中index.js文件内容更改如下,即可运行

//第一步,创建action
const addOne = {
  type: ADD,
  num: 1
}
const addTwo = {
  type: ADD,
  num: 2
}
const square = {
  type: SQUARE
}

//第二步,创建reducer
let math = (state = 10, action) => {
  switch (action.type) {
    case ADD:
      return state + action.num
    case SQUARE:
      return state * state
    default:
      return state
  }
}
//第三步,创建store
import { createStore } from redux
const store = createStore(math)

//第四步,测试,通过dispatch发出action,并通过getState()取得当前state值
console.log(store.getState()) //默认值为10

store.dispatch(addOne) //发起‘+1‘的action
console.log(store.getState()) //当前值为10+1=11

store.dispatch(square) //发起‘乘方‘的action
console.log(store.getState()) //当前值为11*11=121

store.dispatch(addTwo) //发起‘+2‘的action
console.log(store.getState()) //当前值为121+2=123

  结果如下

技术分享图片

 

目录结构

  下面对目录结构进行划分

  1、一般地,将action.type设置为常量,这样在书写错误时,会得到报错提示

// constants/ActionTypes.js
export const ADD = ADD
export const SQUARE = SQUARE

  2、可以将addOne对象和addTwo对象整合成add函数的形式

// action/math.js
import { ADD, SQUARE } from ../constants/ActionTypes
export const add = num => ({ type: ADD, num })
export const square = { type: SQUARE }

  3、根据action.type的分类来拆分reducer,最终通过combineReducers方法将拆分的reducer合并起来。上例中的action类型都是数字运算,无需拆分,只需进行如下变化

// reducer/math.js
import { ADD, SQUARE } from ../constants/ActionTypes
const math = (state = 10, action) => {
  switch (action.type) {
    case ADD:
      return state + action.num
    case SQUARE:
      return state * state
    default:
      return state
  }
}
export default math
// reducer/index.js
import { combineReducers } from redux
import math from ./math
const rootReducer = combineReducers({
  math
})
export default rootReducer

  4、将store存储到store/index.js文件中

// store/index.js
import { createStore } from redux
import rootReducer from ../reducer
export default createStore(rootReducer)

  5、最终,根路径下的index.js内容如下所示

import store from ./store
import {add, square} from ./action/math

console.log(store.getState()) //默认值为10

store.dispatch(add(1)) //发起‘+1‘的action
console.log(store.getState()) //当前值为10+1=11

store.dispatch(square) //发起‘乘方‘的action
console.log(store.getState()) //当前值为11*11=121

store.dispatch(add(2)) //发起‘+2‘的action
console.log(store.getState()) //当前值为121+2=123

  最终目录路径如下所示

技术分享图片

  最终结果如下所示

技术分享图片

 

UI层

  前面的示例中,只是redux的状态改变,下面利用UI层来建立view和state的联系,将根目录下的index.js的内容更改如下

import store from ./store
import React from react
import ReactDOM from react-dom
import { add, square } from ./action/math

ReactDOM.render(
  <div store={store}>
    <p>{store.getState().math}</p>
    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />
    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />
    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />
  </div>,
  document.getElementById(root)
)

  虽然可以显示数字,但是点击按钮时,却不能重新渲染页面

【store.subscribe()】

  接下来介绍store.subscribe()方法了,该方法用来设置监听函数,一旦state发生变化,就自动执行这个函数。该方法的返回值是一个函数,调用这个函数可以解除监听

  下面将示例代码更改如下

import store from ./store
import React from react
import ReactDOM from react-dom
import { add, square } from ./action/math

const render = () => ReactDOM.render(
  <div store={store}>
    <p>{store.getState().math}</p>
    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />
    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />
    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />
  </div>,
  document.getElementById(root)
)

render()
store.subscribe(render)

  代码终于可以正常运行了

 

异步

  redux默认只处理同步,对于API请求这样的异步任务则无能为力

  接下来尝试使用axios的get方法来请求下面这个API

https://jsonplaceholder.typicode.com/posts/2

  获取的数据如下

{
  "userId": 1,
  "id": 2,
  "title": "qui est esse",
  "body": "est rerum tempore vitae\nsequi sint nihil reprehenderit dolor beatae ea dolores neque\nfugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis\nqui aperiam non debitis possimus qui neque nisi nulla"
}

  然后,将其id值设置为state.math的值

  代码修改如下

// constants/ActionTypes.js
export const ADD = ADD
export const SQUARE = SQUARE
export const SET = SET

// action/math.js
import { ADD, SQUARE, SET } from ../constants/ActionTypes
export const add = num => ({ type: ADD, num })
export const square = { type: SQUARE }
export const setNum = num => ({type: SET,num})

// reduce/math.js
import { ADD, SQUARE,SET } from ../constants/ActionTypes
const math = (state = 10, action) => {
  switch (action.type) {
    case ADD:
      return state + action.num
    case SQUARE:
      return state * state
    case SET:
      return action.num
    default:
      return state
  }
}
export default math

// index.js
import store from ./store
import React from react
import ReactDOM from react-dom
import { add, square, setNum } from ./action/math
import axios from axios
let uri = https://jsonplaceholder.typicode.com/posts/2
const render = () => ReactDOM.render(
  <div store={store}>
    <p>{store.getState().math}</p>
    <input type="button" onClick={() => {axios.get(uri).then(res => {store.dispatch(store.dispatch(setNum(res.data.id)))})}} value="设置Num" />
    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />
    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />
    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />
  </div>,
  document.getElementById(root)
)
render()
store.subscribe(render)

  效果如下

  但是,虽然API是异步操作,但store.dispatch并不是异步,而axios通过get方法请求回来数据后,store.dispatch在axios中的then方法中同步取得数据

【redux-thunk】

  如果要使用真正的异步操作,即把axios方法封装到store.dispatch中,需要使用redux-thunk中间件

  首先,使用npm进行安装

npm install --save redux-thunk

  然后,使用applyMiddleware来使用thunk中间件

import { createStore, applyMiddleware } from redux
import thunk from redux-thunk
import rootReducer from ../reducer
export default createStore(rootReducer,applyMiddleware(thunk))

  接着来定义setNum这个action creator,然后在index.js文件的DOM加载完成后就发出setNum

  [注意]如果action是一个对象,则它就是一个action,如果action是一个函数,则它是一个action creator,即action制造器

  修改的代码如下

// action/math.js
import { ADD, SQUARE, SET } from ../constants/ActionTypes
import axios from axios
const uri = https://jsonplaceholder.typicode.com/posts/2
export const add = num => ({ type: ADD, num })
export const square = { type: SQUARE }
export const setNum = () => (dispatch, getState) => {
  return axios.get(uri).then(res => {
    dispatch({
      type: SET,
      num: res.data.id
    })
  })
}

// index.js
import store from ./store
import React from react
import ReactDOM from react-dom
import { add, square, setNum } from ./action/math
const render = () => ReactDOM.render(
  <div store={store}>
    <p>{store.getState().math}</p>
    <input type="button" onClick={() => store.dispatch(setNum())} value="设置Num" />
    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />
    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />
    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />
  </div>,
  document.getElementById(root)
)
render()
store.subscribe(render)

  效果如下

【提示信息】

  如果做的更完备一点,应该把异步请求时的提示信息也加上。增加一个fetch的action,用于控制fetch过程的提示信息及显示隐藏情况

  代码更改如下

// action/fetch.js
import { SET_FETCH_MESSAGE, HIDE_FETCH_MESSAGE } from ../constants/ActionTypes
export const startFetch = { type: SET_FETCH_MESSAGE,message: 开始发送异步请求 }
export const successFetch = { type: SET_FETCH_MESSAGE, message: 成功接收数据 }
export const failFetch = { type: SET_FETCH_MESSAGE, message: 接收数据失败 }
export const hideFetchMessage = { type: HIDE_FETCH_MESSAGE }
// action/math.js
import { ADD, SQUARE, SET } from ../constants/ActionTypes
import { startFetch, successFetch, failFetch, hideFetchMessage } from ./fetch
import axios from axios
const uri = https://jsonplaceholder.typicode.com/posts/2
export const add = num => ({ type: ADD, num })
export const square = { type: SQUARE }
export const setNum = () => (dispatch, getState) => {
  dispatch(startFetch)
  setTimeout(() => {
    dispatch(hideFetchMessage)
  }, 500)
  return axios
    .get(uri)
    .then(res => {
      setTimeout(() => {
        dispatch(successFetch)
        setTimeout(() => {
          dispatch(hideFetchMessage)
        }, 500)
        dispatch({ type: SET, num: res.data.id })
      }, 1000)
    })
    .catch(err => {
      dispatch(failFetch)
      setTimeout(() => {
        dispatch(hideFetchMessage)
      }, 500)
    })
}
// constants/ActionTypes.js
export const ADD = ADD
export const SQUARE = SQUARE
export const SET = SET
export const SET_FETCH_MESSAGE = SET_FETCH_MESSAGE
export const HIDE_FETCH_MESSAGE = HIDE_FETCH_MESSAGE
// reduce/fetch.js
import { SET_FETCH_MESSAGE,HIDE_FETCH_MESSAGE } from ../constants/ActionTypes
const initState = {
  message:‘‘,
  isShow:false
}
const fetch = (state = initState, action) => {
  switch (action.type) {
    case SET_FETCH_MESSAGE:
      return {isShow: true, message: action.message}
    case HIDE_FETCH_MESSAGE:
      return { isShow: false, message: ‘‘ }
    default:
      return state
  }
}
export default fetch
// index.js
import store from ./store
import React from react
import ReactDOM from react-dom
import { add, square, setNum } from ./action/math
const render = () => ReactDOM.render(
  <div store={store}>
    <p>{store.getState().math}</p>
    <input type="button" onClick={() => store.dispatch(setNum())} value="设置Num" />
    <input type="button" onClick={() => store.dispatch(add(1))} value="+1" />
    <input type="button" onClick={() => store.dispatch(add(2))} value="+2" />
    <input type="button" onClick={() => store.dispatch(square)} value="乘方" />
    {store.getState().fetch.isShow && <p>{store.getState().fetch.message}</p>}
  </div>,
  document.getElementById(root)
)
render()
store.subscribe(render)

  效果如下

  

展示和容器

  下面来介绍react-redux。前面的代码中,我们是通过store.subscribe()方法监控state状态的变化来更新UI层的。而使用react-redux,可以让组件动态订阅状态树。状态树一旦被修改,组件能自动刷新显示最新数据

  react-redux将所有组件分成两大类:展示组件和容器组件。展示组件只负责UI呈现,所有数据由参数props提供;容器组件则负责管理数据和业务逻辑,带有内部状态,可使用redux的API。要使用react-redux,就要遵守它的组件拆分规范

【provider】

  react-redux提供Provider组件,可以让容器组件默认可以拿到state,而不用当容器组件层级很深时,一级级将state传下去

  将index.js文件更改如下

// index.js
import React from react
import ReactDOM from react-dom
import store from ./store
import MathContainer from ./container/MathContainer
import { Provider } from react-redux
ReactDOM.render(
  <Provider store={store}>
    <MathContainer />
  </Provider>,
  document.getElementById(root)
)

  按照组件拆分规范,将原来index.js中相关代码,分拆到container/MathContainer和component/Math这两个组件中

【connect】

  react-redux提供connect方法,用于从展示组件生成容器组件。connect的意思就是将这两种组件连接起来

import { connect } from react-redux
const MathContainer = connect()(Math);

  Math是展示组件,MathContainer就是由React-redux通过connect方法自动生成的容器组件

  为了定义业务逻辑,需要给出下面两方面的信息

  1、输入逻辑:外部的数据(即state对象)如何转换为展示组件的参数

  2、输出逻辑:用户发出的动作如何变为Action对象,从展示组件传出去

  因此,connect方法的完整API如下

import {connect} from react-redux
const MathContainer= connect(
    mapStateToProps,
    mapDispatchToProps
)(Math)

  上面代码中,connect方法接受两个参数:mapStateToProps和mapDispatchToProps。它们定义了展示组件的业务逻辑。前者负责输入逻辑,即将state映射到UI组件的参数(props),后者负责输出逻辑,即将用户对展示组件的操作映射成Action

【mapStateToProps()】

  mapStateToProps建立一个从外部的state对象到展示组件的props对象的映射关系。作为参数,mapStateToProps执行后应该返回一个对象,里面的每一个键值对就是一个映射。

const mapStateToProps = (state) => {
  return {
    num: getNum(state)                  
  }  
}

  mapStateToProps的第一个参数总是state对象,还可以使用第二个参数,代表容器组件的props对象。使用ownProps作为参数后,如果容器组件的参数发生变化,也会引发展示组件重新渲染

const mapStateToProps = (state,ownProps) => {
  return {
    num: getNum(state)                  
  }  
}

  mapStateToProps会订阅Store,每当state更新的时候,就会自动执行,重新计算展示组件的参数,从而触发展示组件的重新渲染。connect方法可以省略mapStateToProps参数,那样,展示组件就不会订阅Store,就是说Store的更新不会引起展示组件的更新

【mapDispatchToProps】

  mapDispatchToProps是connect函数的第二个参数,用来建立展示组件的参数到store.dispatch方法的映射。也就是说,它定义了用户的哪些操作应该当作action,传给Store。它可以是一个函数,也可以是一个对象

  如果mapDispatchToProps是一个函数,会得到dispatch和ownProps(容器组件的props对象)两个参数

const mapDispatchToProps = (dispatch,ownProps) => {
  return {
    onSetNumClick: () => dispatch(setNum())
  }
}

  mapDispatchToProps作为函数,应该返回一个对象,该对象的每个键值对都是一个映射,定义了展示组件的参数怎样发出action

  如果mapDispatchToProps是一个对象,它的每个键名也是对应展示组件的同名参数,键值应该是一个函数,会被当作action creator,返回的action会由redux自动发出

  因此,上面的写法简写如下所示

const mapDispatchToProps = {
  onsetNumClick: () => setNum()
}

 

最终结构

  由于store目录中,只能一个index.js文件,且不会有内容扩展,将其更改为根目录下的store.js文件

  将其他的目录都变成复数形式,最终的目录结构如下所示

技术分享图片

  效果如下

  详细代码如下所示,且可访问github线上地址

【components】

// components/Math.js
import React from react
const Math = ({
  num,
  isShow,
  fetchMessage,
  onSetNumClick,
  onAddOneClick,
  onAddTwoClick,
  onSqureClick
}) => (
  <section>
    <p>{num}</p>
    <input type="button" onClick={onSetNumClick} value="设置Num" />
    <input type="button" onClick={onAddOneClick} value="+1" />
    <input type="button" onClick={onAddTwoClick} value="+2" />
    <input type="button" onClick={onSqureClick} value="乘方" />
    {isShow && <p>{fetchMessage}</p>}
  </section>
)

export default Math

【containers】

// containers/MathContainer.js
import { connect } from react-redux
import Math from ../components/Math
import { getNum } from ../selectors/math
import { getFetchMessage, getFetchIsShow } from ../selectors/fetch
import { setNum, add, square } from ../actions/math
const mapStateToProps = state => {
  return {
    num: getNum(state),
    fetchMessage: getFetchMessage(state),
    isShow: getFetchIsShow(state)
  }
}
const mapDispatchToProps = {
  onSetNumClick: () => setNum(),
  onAddOneClick: () => add(1),
  onAddTwoClick: () => add(2),
  onSqureClick: () => square
}
const MathContainer = connect(mapStateToProps, mapDispatchToProps)(Math)
export default MathContainer

【actions】

// actions/fetch.js
import { SET_FETCH_MESSAGE, HIDE_FETCH_MESSAGE } from ../constants/ActionTypes
export const startFetch = { type: SET_FETCH_MESSAGE,message: 开始发送异步请求 }
export const successFetch = { type: SET_FETCH_MESSAGE, message: 成功接收数据 }
export const failFetch = { type: SET_FETCH_MESSAGE, message: 接收数据失败 }
export const hideFetchMessage = { type: HIDE_FETCH_MESSAGE }
// actions/math.js
import { ADD, SQUARE, SET } from ../constants/ActionTypes
import { startFetch, successFetch, failFetch, hideFetchMessage } from ./fetch
import axios from axios
const uri = https://jsonplaceholder.typicode.com/posts/2
export const add = num => ({ type: ADD, num })
export const square = { type: SQUARE }
export const setNum = () => (dispatch, getState) => {
  dispatch(startFetch)
  setTimeout(() => {dispatch(hideFetchMessage)}, 300)
  return axios
    .get(uri)
    .then(res => {
      dispatch(successFetch)
      setTimeout(() => {dispatch(hideFetchMessage)}, 300)
      dispatch({ type: SET, num: res.data.id })
    })
    .catch(err => {
      dispatch(failFetch)
      setTimeout(() => {dispatch(hideFetchMessage)}, 300)
    })
}

【constants】

// constants/ActionTypes.js
export const ADD = ADD
export const SQUARE = SQUARE
export const SET = SET
export const SET_FETCH_MESSAGE = SET_FETCH_MESSAGE
export const HIDE_FETCH_MESSAGE = HIDE_FETCH_MESSAGE

【reducers】

// reducers/fetch.js
import { SET_FETCH_MESSAGE,HIDE_FETCH_MESSAGE } from ../constants/ActionTypes
const initState = {
  message:‘‘,
  isShow:false
}
const fetch = (state = initState, action) => {
  switch (action.type) {
    case SET_FETCH_MESSAGE:
      return {isShow: true, message: action.message}
    case HIDE_FETCH_MESSAGE:
      return { isShow: false, message: ‘‘ }
    default:
      return state
  }
}
export default fetch
// reducers/index.js
import { combineReducers } from redux
import math from ./math
import fetch from ./fetch
const rootReducer = combineReducers({
  math,
  fetch
})

export default rootReducer
// reduces/math.js
import { ADD, SQUARE,SET } from ../constants/ActionTypes
const math = (state = 10, action) => {
  switch (action.type) {
    case ADD:
      return state + action.num
    case SQUARE:
      return state * state
    case SET:
      return action.num
    default:
      return state
  }
}
export default math

【selectors】

// selectors/fetch.js
export const getFetchMessage = state => state.fetch.message
export const getFetchIsShow = state => state.fetch.isShow
// selectors/math.js
export const getNum = state => state.math

【根目录】

// index.js
import React from react
import ReactDOM from react-dom
import store from ./store
import MathContainer from ./containers/MathContainer
import { Provider } from react-redux
ReactDOM.render(
  <Provider store={store}>
    <MathContainer />
  </Provider>,
  document.getElementById(root)
)
// store.js
import { createStore, applyMiddleware } from redux
import thunk from redux-thunk
import rootReducer from ./reducers
export default createStore(rootReducer,applyMiddleware(thunk))

 

redux简明学习

标签:state   文件内容   roo   contain   class   时间   tps   hub   height   

原文:https://www.cnblogs.com/xiaohuochai/p/8447826.html

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