如何在 React Redux 中访问商店 state？

Question

I am just making a simple app to learn async with redux. I have gotten everything working, now I just want to display the actual state onto the web-page. Now, how do I actually access the store's state in the render method?

Here is my code (everything is in one page because I'm just learning):

const initialState = {
        fetching: false,
        fetched: false,
        items: [],
        error: null
    }

const reducer = (state=initialState, action) => {
    switch (action.type) {
        case "REQUEST_PENDING": {
            return {...state, fetching: true};
        }
        case "REQUEST_FULFILLED": {
            return {
                ...state,
                fetching: false,
                fetched: true,
                items: action.payload
            }
        }
        case "REQUEST_REJECTED": {
            return {...state, fetching: false, error: action.payload}   
        }
        default: 
            return state;
    }
};

const middleware = applyMiddleware(promise(), thunk, logger());
const store = createStore(reducer, middleware);

store.dispatch({
    type: "REQUEST",
    payload: fetch('http://localhost:8000/list').then((res)=>res.json())
});

store.dispatch({
    type: "REQUEST",
    payload: fetch('http://localhost:8000/list').then((res)=>res.json())
});

render(
    <Provider store={store}>
        <div>
            { this.props.items.map((item) => <p> {item.title} </p> )}
        </div>
    </Provider>,
    document.getElementById('app')
);

So, in the render method of the state I want to list out all the item.title from the store.

Thanks

Answer 1

You should create separate component, which will be listening to state changes and updating on every state change:

import store from '../reducers/store';

class Items extends Component {
  constructor(props) {
    super(props);

    this.state = {
      items: [],
    };

    store.subscribe(() => {
      // When state will be updated(in our case, when items will be fetched), 
      // we will update local component state and force component to rerender 
      // with new data.

      this.setState({
        items: store.getState().items;
      });
    });
  }

  render() {
    return (
      <div>
        {this.state.items.map((item) => <p> {item.title} </p> )}
      </div>
    );
  }
};

render(<Items />, document.getElementById('app'));

Answer 2

Import connect from react-redux and use it to connect the component with the state connect(mapStates,mapDispatch)(component)

import React from "react";
import { connect } from "react-redux";


const MyComponent = (props) => {
    return (
      <div>
        <h1>{props.title}</h1>
      </div>
    );
  }
}

Finally you need to map the states to the props to access them with this.props

const mapStateToProps = state => {
  return {
    title: state.title
  };
};
export default connect(mapStateToProps)(MyComponent);

Only the states that you map will be accessible via props

Check out this answer: https://stackoverflow.com/a/36214059/4040563

For further reading : https://medium.com/@atomarranger/redux-mapstatetoprops-and-mapdispatchtoprops-shorthand-67d6cd78f132

Answer 3

You need to use Store.getState() to get current state of your Store.

For more information about getState() watch this short video.

Answer 4

You want to do more than just getState . You want to react to changes in the store.

If you aren't using react-redux, you can do this:

function rerender() {
    const state = store.getState();
    render(
        <div>
            { state.items.map((item) => <p> {item.title} </p> )}
        </div>,
        document.getElementById('app')
    );
}

// subscribe to store
store.subscribe(rerender);

// do initial render
rerender();

// dispatch more actions and view will update

But better is to use react-redux. In this case you use the Provider like you mentioned, but then use connect to connect your component to the store.

Answer 5

If you want to do some high-powered debugging, you can subscribe to every change of the state and pause the app to see what's going on in detail as follows.

store.js

 store.subscribe( () => { console.log('state\\n', store.getState()); debugger; });

Place that in the file where you do createStore .

To copy the state object from the console to the clipboard, follow these steps:

1. Right-click an object in Chrome's console and select Store as Global Variable from the context menu. It will return something like temp1 as the variable name.

2. Chrome also has a copy() method, so copy(temp1) in the console should copy that object to your clipboard.

https://stackoverflow.com/a/25140576

https://scottwhittaker.net/chrome-devtools/2016/02/29/chrome-devtools-copy-object.html

You can view the object in a json viewer like this one: http://jsonviewer.stack.hu/

You can compare two json objects here: http://www.jsondiff.com/

Answer 6

All of the answers are from pre-hook era. You should use useSelector-hook to get the state from redux.

In your redux-reducer file or somewhere where you can import it easily:

import { useSelector } from 'react-redux'

export function useEmployees() {
  return useSelector((state) => state.employees)
}

In your application code:

const { employees } = useEmployees()

More information on redux-hooks: https://react-redux.js.org/api/hooks to accomplish this goal.

Answer 7

HACK SOLUTION : Example from my REAL project . Save Redux store objects to external JSON file

STEP-1 import useStore first from react-redux and then getState() function is used to access store state.

STEP-2 area is the name of my slice in Redux store and areaName is state in that slice.

STEP-3 FiletoSave variable is used to export JSON file with data from store.

import { useStore } from "react-redux";

const exportJsonFileFromStore = () => {

const store = useStore();
const FileSaver = require('file-saver');    
    
function exportData() {
   
    const filename = 'filter_settings';

    let prepareObject = {       // It is used to make a JSON object 
      areaName:store.getState().area.areaName  ,   
    }
    const fileToSave = new Blob([JSON.stringify(prepareObject)], {
        type: 'application/json'
    });
    // this will save file
    FileSaver.saveAs(fileToSave, filename);
}

return (
  
        <button onClick={(event: any) => exportData()}>Click me to download!</button>
   
)

}

Answer 8

import { ReactReduxContext } from 'react-redux';

var store = useContext(ReactReduxContext).store.getState();

console.log(store);

https://react-redux.js.org/using-react-redux/accessing-store#using-reactreduxcontext-directly