react-native 中的 UseSelector 返回未定义，但 redux 中的变量已更新

Question

i have trying to using UseSelector to get data in a redux, but it's alwas returned undefined, but when i try log console.log teh variable that i wanted to get in redux it's get updated, but when i try console log the useSelector it's returned undefined

code Redux :

export const EXCHAHNGETOSECOND = 'EXCHANGETOSECOND'

export const exchangetosecwork = (hour,minute,second) =>({
    type:EXCHAHNGETOSECOND,
    payloadhourwork : hour,
    payloadminutework : minute,
    payloadsecondwork : second
})

let initialState ={
    resultWorkinSecond : 0
}

export const mainReducer = (state=initialState, action) =>{
    switch (action.type) {
        case EXCHAHNGETOSECOND:
            const hourTosecond = action.payloadhourwork * 3600
            const minuteTosecond = action.payloadminutework * 60
            const res = hourTosecond+minuteTosecond+action.payloadsecondwork
            state.resultWorkinSecond = res
            console.log(state.resultWorkinSecond);
            return state.resultWorkinSecond
        default:
            return state
    }
}

export default mainReducer

store redux :

import { createStore } from "redux";
import mainReducer from "./redux";
import AsyncStorage from '@react-native-async-storage/async-storage';
import { persistStore, persistReducer } from 'redux-persist'


const persistConfig={
    key:'root',
    storage:AsyncStorage,
};

const persistedReducer = persistReducer(persistConfig,mainReducer)

export default() => {
    let store = createStore(persistedReducer)
    let persistor = persistStore(store)
    return{ store, persistor }
}

myConsole log test:

 const resWorkinSec = useSelector((state)=>state.resultWorkinSecond)
    
    <Pressable onPress={()=>{
                            dispatch(exchangetosecwork(hour,minute,second))
                            console.log(resWorkinSec)
                        }}>

[console log result 1

Answer 1

Your reducer has multiple bugs:

• it does an assignment, changing state. This is not allowed in legacy Redux reducers, but only in modern Redux using createSlice
• return state.resultWorkinSecond then even changes the full state structure.

Correct legacy Redux code would look like this:

export const mainReducer = (state=initialState, action) =>{
    switch (action.type) {
        case EXCHAHNGETOSECOND:
            const hourTosecond = action.payloadhourwork * 3600
            const minuteTosecond = action.payloadminutework * 60
            const res = hourTosecond+minuteTosecond+action.payloadsecondwork
            return { ...state, resultWorkinSecond: res }
        default:
            return state
    }
}

All that said, this is an old style of Redux that we do not recommend any more since 2019. It is more complicated, and error-prone. And about 4 times the code modern Redux would be. Modern Redux does not use switch..case reducers, ACTION_TYPES, immtuable reducer logic (like you needed to do here), createStore and the likes.

I would highly recommend you drop what you are doing for a moment and go through the official Redux tutorial .