redux provider源碼解析

provider 源碼

import { Component, Children } from 'react'
import PropTypes from 'prop-types'
import storeShape from '../utils/storeShape'
import warning from '../utils/warning'
let didWarnAboutReceivingStore = false

function warnAboutReceivingStore() {
  if (didWarnAboutReceivingStore) {
    return
  }
  didWarnAboutReceivingStore = true
  warning(
    '<Provider> does not support changing `store` on the fly. ' +
    'It is most likely that you see this error because you updated to ' +
    'Redux 2.x and React Redux 2.x which no longer hot reload reducers ' +
    'automatically. See https://github.com/reactjs/react-redux/releases/' +
    'tag/v2.0.0 for the migration instructions.'
  )
}

export default class Provider extends Component {
  getChildContext() {
    return { store: this.store }
  }

  constructor(props, context) {
    super(props, context)
    this.store = props.store
  }

  render() {
    return Children.only(this.props.children)
  }
}

if (process.env.NODE_ENV !== 'production') {
  Provider.prototype.componentWillReceiveProps = function (nextProps) {
    const { store } = this
    const { store: nextStore } = nextProps

    if (store !== nextStore) {
      warnAboutReceivingStore()
    }
  }
}

Provider.propTypes = {
  store: storeShape.isRequired,
  children: PropTypes.element.isRequired
}
Provider.childContextTypes = {
  store: storeShape.isRequired
}

首先學習react數據傳遞三種方法，props，state，context

props：通常用於將父組件數據傳遞到子組件，不能跨組件傳遞

state：state是內部狀態或者局部狀態
           es6數據解析操做，let {xxx ,xx, x} = this.state;

context: 和props相比，context能夠跨組件傳遞信息

聲明context步驟一：

constructor(props, context) {
    super(props, context)
    this.store = props.store
  }

getChildContext() {
    return { store: this.store }
  }

更具react生命週期，首先constructor方法獲取屬性store，getChildContext()將store放入context中

步驟二：

Provider.propTypes = {
  store: storeShape.isRequired,
  children: PropTypes.element.isRequired
}

驗證組件信息

步驟三：

Provider.childContextTypes = {
  store: storeShape.isRequired
}

聲明瞭childrenContextTypes。若是不聲明的話，將沒法在組件中使用getChildContext()方法；

獲取context：

子樹中的任何組件均可以經過定義ContextTypes 去訪問它。

connect中經過

  Connect.contextTypes = {

      store: storeShape

    }

而後經過constructor獲取store 

constructor(props, context) {

        super(props, context)

        this.version = version

        this.store = props.store || context.store

         const storeState = this.store.getState()

        this.state = { storeState }

        this.clearCache()

      }

最後執行render渲染，返回一個react子元素。Children.only是react提供的方法，this.props.children表示的是隻有一個root的元素。