React-Redux组件不反映Redux Store中的更改

Question

I am new to Redux and i've been having a hard time rendering changes made to the store. I've been using Redux-DevTools to explore state changes and here is my problem.

I have a sidebar which has expanded state as true/false. Initial state is below.

{expanded: false}

During the toggle action i trigger store.dispatch to change the state to true. In React-DevTools i could see that my state is being changed, the console also logs the change when executed from within my sidenav component.

I have a home page which is able to fetch the initial state of the store, however the actions from sidenav which updates the store doesn't re-render(props val dint change) the home page.

I strongly feel the issue is related to this SO post but not able to get around the wrapped component concept. Any advice.

React Redux - changes aren't reflected in component

Below is code.

Redux Store

const rootReducer = combineReducers({
    sideBarReducerMain: sidebarReducer })

export const configurestore = () => {
    const store = createStore(rootReducer, composeWithDevTools(
      ));

    return store; }

Action generators

export const onExpand = {
    type: 'EXPAND',
    payload: {
        expanded: true
    }
}

export const onCollapse = {
    type: 'COLLAPSE',
    payload: {
        expanded: false
    }
}

Reducer

export const sidebarReducer = (state = {expanded:false},action) => {
 switch (action.type) {
     case 'EXPAND':
        return Object.assign({}, state, {expanded: true})
     case 'COLLAPSE':
        return Object.assign({}, state, {expanded: false})
    default:
        return state;   
 }
}

SideBar Toggle (The console logs the new state on every toggle)

onToggle = (expanded) => {

    expanded ? store.dispatch(onExpand):store.dispatch(onCollapse)
    this.setState({ expanded: expanded });

    //outputs the state change looks fine.
    console.log("State of store :: " + store.getState());

};

Home page

import React from 'react';
import styled from 'styled-components'
import Main from './MainAlign'
import { connect } from 'react-redux'

class HomePage extends React.Component {


 getExpansionState() {
  console.log("From render" + this.props.expandedState)
    return this.props.expandedState
 }

 componentWillReceiveProps(nextProps) {
  console.log("Looks like this never gets called :( " + this.props.expandedState)
}


  render(props) {

      return (
        <div>
        <Main expanded={this.getExpansionState()}>
        <h1>Welcome</h1>
        <p>This is my site. Take a look around!</p>
        </Main>  
        </div>
      )


  }

}

const mapStateToProps = state => {
  console.log("New state " + state.expanded)
  return {
    expandedState: state.expanded
  }
}

export default connect(mapStateToProps)(HomePage);

REDUX DevTools

Answer 1

You need to declare action creators (functions) which return actions (objects):

export const onExpand = () => ({
  type: "EXPAND",
  payload: {
    expanded: true
  }
});

Then instead of calling store.dispatch , you should connect the action creator:

withRouter(connect(null, { onExpand, onCollapse })(SideBar))

And invoke it in your component:

if (expanded) {
  this.props.onExpand();
} else {
  this.props.onCollapse();
}

Working code:

Misc

this.setState({ expanded: expanded });
console.log("FROM SIDENAV" + this.state.expanded);

setState is asynchronous so you need use the callback to access the updated value:

this.setState({ expanded }, () => console.log("FROM SIDENAV" + this.state.expanded));

Also, there's no need to replicate the redux state in local component (single source of truth).

You can also combine onExpand and onCollapse into a single onToggle function and perform the toggle in reducer: expanded: !state.expanded , or pass the expanded flag as payload.

Answer 2

Change your mapStateToProps function like that:

const mapStateToProps = state => {
  console.log("New state " + state.expanded)
  return {
    expandedState: state.sideBarReducerMain.expanded
  }
}

You have a sideBarReducerMain state in your root,global state. This sideBarRecuerMain state has an expanded value not the global one.

Also, you don't need a payload for your action creators since you don't use them. Just a type is enough for your logic.