redux初始化state时，在reducers.js文件的参数action.type有什么用？action怎么传递的？

Question

http://redux.js.org/docs/adva...

import React, { Component } from 'react'
import { Provider } from 'react-redux'
import configureStore from '../configureStore'
import AsyncApp from './AsyncApp'

// 从 configureStore.js 获取初始化 store
const store = configureStore()

// Provider 接受Redux的store作为 props 并将其声明为context的属性之一
// 子组件可以在声明了contextTypes之后，通过this.context.store访问到store

export default class Root extends Component {
    render() {
        return (
            <Provider store={store}>
                <AsyncApp />
            </Provider>
        )
    }
}

configureStore.js

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

const loggerMiddleware = createLogger()

// rootReducer 构造最原始的 store
// 寻找 reducer
export default function configureStore(preloadedState) {
    return createStore(
        rootReducer,
        preloadedState,
        applyMiddleware(
            thunkMiddleware,
            loggerMiddleware
        )
    )
}

reducers.js

import { combineReducers } from 'redux'
import {
  SELECT_SUBREDDIT,
  INVALIDATE_SUBREDDIT,
  REQUEST_POSTS,
  RECEIVE_POSTS
} from './actions'

function selectedSubreddit(state = 'reactjs', action) {
  switch (action.type) {
    case SELECT_SUBREDDIT:
      return action.subreddit
    default:
      return state
  }
}

function posts(
  state = {
    isFetching: false,
    didInvalidate: false,
    items: []
  },
  action
) {
  switch (action.type) {
    case INVALIDATE_SUBREDDIT:
      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 postsBySubreddit(state = {}, action) {
  switch (action.type) {
    case INVALIDATE_SUBREDDIT:
    case RECEIVE_POSTS:
    case REQUEST_POSTS:
      return Object.assign({}, state, {
        [action.subreddit]: posts(state[action.subreddit], action)
      })
    default:
      return state
  }
}

const rootReducer = combineReducers({
  postsBySubreddit,
  selectedSubreddit
})

export default rootReducer

Answer 1

reducer的作用是返回新的state。它根据action.type判断对state采取怎样的操作， 返回新的state。

action其实就是一个对象，当你要触发reducer时就需要传递这个对象，根据它的type属性对state进行处理。

可以看一下我今天刚写的这篇文章