如何在 redux 调度完成时正确获取，然后渲染组件

Question

. Answers to this question are eligible for a +500 reputation bounty. slevin wants to to this question:

please help a react newbie understand what's going on

I use react 18.2.0, redux 4.2.0 and redux thunk

I want to wait until my dispatch is done, so I can take the data it got from the server and render a component with that data

I try to do the following in my component:

import store from '../redux/store'; 

const featureInfoA = useSelector(featureInfo) 
const featureErrorA = useSelector(featureError) 
const featureStatusA = useSelector(featureStatus) 
    
const clickFeatureFromList = (id) =>  { 
  //start dispatching
  dispatch(fetchFeatureInfoById({ id, category })) 
    .then((e) => {
      console.log('BINGO THEN ', featureInfoA, featureErrorA, featureStatusA);
    })
}

//check store when a specific state changed and then get its data and render a component
store.subscribe(() => {
  const state = store.getState()
  if (state.features.status == 'succeeded' || state.features.status == 'failed') {
    console.log('BINGO SUBSCRIBE ', featureInfoA);
    accordionDetailsRootGlobal.render(<ContextInfo featureData={featureInfoA} />);
  } 
})

The issue is that in my console I see:

• BINGO SUBSCRIBE a multiple times
• and then the DATA from store that is inside the store
• and then the BINGO THEN a null idle that is in the then after calling dispatch

I think that the log of the store should be first

Why I see "BINGO SUBSCRIBE a" that is inside the store.subscribe multiple times?

Why I never see the final data that came from the server? "BINGO THEN a null idle" contains the initial state, even though "DATA from store" brought back data.

By the way, this my store, for features

import { createSlice, createAsyncThunk } from '@reduxjs/toolkit'

const FEATURE_URL = 'http://localhost:3500/map'

//status : idle, loading, succeeded, failed
const initialState = {
    info:'a',
    status:'idle',
    error:null
}

export const fetchFeatureInfoById = createAsyncThunk('feature/fetchInfoById', (originalData) => {
    console.log('fetchFeatureInfoById originalData ', originalData);
    fetch(FEATURE_URL + '/feature/' + originalData.id + '/' + originalData.category)
    .then((response) => response.json())
    .then((data) => {
        console.log('DATA from store ', data);
        return data;
    })
    .catch((error) => {
        return error.message;
    });
})

export const featuresSlice = createSlice({
    name: 'features',
    initialState,
    reducers: { 
        featureInfoById: {
            reducer(state, action) {
                //do something with the id 
                console.log('feature state ', ' -- state : ',state.status, ' -- action : ', action);
            },
            prepare(category, id) {
                return{
                    payload:{
                        category,
                        id
                    }
                }
            }
        }
    },
    extraReducers(builder) {
        builder
        .addCase(fetchFeatureInfoById.pending, (state, action) => {
            state.status = 'loading'
        })
        .addCase(fetchFeatureInfoById.rejected, (state, action) => {
            state.status = 'failed'
            state.error = action.error.message
        })
        .addCase(fetchFeatureInfoById.fulfilled, (state, action) => {
            console.log('fulfilled data store ', state, action);
            state.status = 'succeeded'
            state.info = action.palyload
        })
    }
  }) 
   
  export const featureInfo = (state) => state.features.info;
  export const featureError = (state) => state.features.error;
  export const featureStatus = (state) => state.features.status;
  export const {featureInfoById} = featuresSlice.actions
  export default featuresSlice.reducer

I just want to get the data after the dispatch is done, to render a component with them. Please help me understand what I am doing wrong and how can I fix that.

Answer 1

You don't need to do the store.subscribe thing.

The selector is supposed to update and it will cause a render of your component. So, initially featureInfoA is undefined but after the promise is resolved it will update the store which will trigger a render in your component

import store from '../redux/store'; 

const featureInfoA = useSelector(featureInfo) 
const featureErrorA = useSelector(featureError) 
const featureStatusA = useSelector(featureStatus) 
    
const clickFeatureFromList =(id) =>  { 
  //start dispatching
  dispatch(fetchFeatureInfoById({id, category})) 
}

// add some logic here to check if featureInfoA has value
if(featureErrorA) return <div>Error</div>

if(featureStatusA === "loading") return <div>Loading...</div>

if(featureInfoA) return <div>{featureInfoA}</div>

Answer 2

Why I see "BINGO SUBSCRIBE a" that is inside the store.subscribe multiple times?

That is because, as the docs mention this

Adds a change listener. It will be called any time an action is dispatched, and some part of the state tree may potentially have changed.

So basically each time any action is dispatched and any part of the state tree might have been changed it will be triggered. This refers to your entire store (not just featuresSlice )

---

Why I never see the final data that came from the server? "BINGO THEN a null idle" contains the initial state, even though "DATA from store" brought back data.

This is most likely because your fetchFeatureInfoById is not returning anything (please note that the return data; part is inside a callback, but the main function doesn't return anything) so in your extra reducer action.payload has no value.

So what you want to do in order to be able to properly set the slice state from the slice extra reducer is returning the fetch result from the fetchFeatureInfoById function. So basically your function would look something like:

export const fetchFeatureInfoById = createAsyncThunk('feature/fetchInfoById', (originalData) => {
    console.log('fetchFeatureInfoById originalData ', originalData);
    // Add the return keyword before the fetch from the next line
    return fetch(FEATURE_URL + '/feature/' + originalData.id + '/' + originalData.category)
    .then((response) => response.json())
    .then((data) => {
        console.log('DATA from store ', data);
        return data;
    })
    .catch((error) => {
        return error.message;
    });
})

---

PS: Without a reproducible example is not 100% this will fix all your problems, but it should at the very least point you in the right direction.

---

Extra suggestion (related to the other answer):

I think you can at least use an useEffect? It would be way more efficient to only trigger the an effect when accordionDetailsRootGlobal changes or featureInfoA (so basically have an useEffect with this 2 dependencies and render the ContextInfo when one of this 2 change, rather than rendering on every store update). Something like:

  useEffect(() => {
    if (featureInfoA)
      accordionDetailsRootGlobal.render(<ContextInfo featureData={featureInfoA} />)
  }, [accordionDetailsRootGlobal, featureInfoA])

Answer 3

I Think this might be a better approach to deal with dispatch when you want to observe your data after you request successfully handled

   const clickFeatureFromList =async (id) =>  { 
    
      //start dispatching
     const result = await dispatch(fetchFeatureInfoById({ id, category }))
     if (fetchFeatureInfoById.fulfilled.match(result)) { 
     const {payload} = result
     console.log('BINGO THEN ', featureInfoA, featureErrorA, featureStatusA);

   }
    }