Reactjs useReducer:无法使用userReducer获取初始状态

我已经实现了useReducer，以根据操作类型分派操作，并且每次我根据操作类型更新状态变量时，都会在尝试读取初始状态时出错。也许我的代码可以解释更多

尝试读取initialLoginState.isLoading时出错

App.js代码：

import * as React from 'react';
import { NavigationContainer } from '@react-navigation/native';
import BottomNavigation from './src/Navigations/BottomNavigation';
import AuthStackNavigation from './src/Navigations/AuthStackNavigation'
import { useState, useEffect, useMemo, useReducer } from 'react';
import { View } from 'react-native-animatable';
import { ActivityIndicator } from 'react-native';
import { AuthenticationContext } from './src/context/AuthenticationContext'

export default function App() {

  //Initial state values
  const initialLoginState = {
    isLoading: false,
    userName: null,
    userToken: null
  }

//Reducer function
  const loginReducer = (action, prevState) => {
    switch (action.type) {
      case 'LOGIN':
        return {
          ...prevState,
          userToken: action.token,
          userName: action.id,
          isLoading: false
        };
      case 'LOGOUT':
        return {
          ...prevState,
          userName: null,
          userToken: null,
          isLoading: false,
        };
      case 'REGISTER':
        return {
          ...prevState,
          userToken: action.token,
          userName: action.id,
          isLoading: false,
        };
      case 'RETRIEVE_TOKEN ':
        return {
          ...prevState,
          userToken: action.token,
          isLoading: false
        };
    }
  }

  //Defining useReducer
  const [newLoginState, dispatch] = useReducer(loginReducer, initialLoginState);
  const authContext = useMemo(() => ({
    signIn: (email, password) => {
      // setUserToken('abc');
      // setIsLoading(false);

      console.log("called")
      let userToken
      userToken = null;
      if (email == 'user' && password == 'pass') {
        userToken = 'abc';
      }
      dispatch({ type: 'RETRIEVE_TOKEN', id: email, token: userToken })
    },
    signOut: () => {
      dispatch({ type: 'LOGOUT', })
    },
    signUp: () => {
      setUserToken(null);
      setIsLoading(false);
    }

  }), []);

  useEffect(() => {
    let userToken;
    userToken = "dfsdfsdf"
    dispatch({ type: 'REGISTER', token: userToken })
  }, [])

  if (initialLoginState.isLoading) {
    return (
      <View style={{ flex: 1, justifyContent: 'center', alignContent: 'center' }}>
        <ActivityIndicator size='large'></ActivityIndicator>
      </View>
    )
  }

  return (
    <AuthenticationContext.Provider value={authContext}>
      <NavigationContainer>
        {initialLoginState.userToken !== null ?
          <BottomNavigation />
          :
          <AuthStackNavigation />
        }
      </NavigationContainer>
    </AuthenticationContext.Provider>

  );
}

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首先，减速机功能开关中的默认情况丢失

---

第二，你能把整个组件代码（只是需要的部分！）放进去吗？因为即使没有默认的大小写，我运行你的代码也没有问题

尝试将reducer函数更新为此（翻转参数！）：

---

不要忘记默认情况

谢谢你的回复。我已经为您的参考更新了完整的代码。发布组件代码作为整体，而不是从这里和那里，这样我们就可以看到发生了什么！我已经更新了entier App.js文件。请看一下。非常感谢您的帮助。它真的耍了一个花招。只需交换参数，就可以很好地工作。不客气，默认情况下不要忘记：）是的，我添加了它

TypeError: undefined is not an object (evaluating 'newLoginState.isLoading')
- node_modules/react-native/Libraries/LogBox/LogBox.js:148:8 in registerError
- node_modules/react-native/Libraries/LogBox/LogBox.js:59:8 in errorImpl
- node_modules/react-native/Libraries/LogBox/LogBox.js:33:4 in console.error

//Reducer function
//-  const loginReducer = (action, prevState) => {
  const loginReducer = (prevState, action) => {
    switch (action.type) {
      case 'LOGIN':
        return {
          ...prevState,
          userToken: action.token,
          userName: action.id,
          isLoading: false
        };
      case 'LOGOUT':
        return {
          ...prevState,
          userName: null,
          userToken: null,
          isLoading: false,
        };
      case 'REGISTER':
        return {
          ...prevState,
          userToken: action.token,
          userName: action.id,
          isLoading: false,
        };
      case 'RETRIEVE_TOKEN ':
        return {
          ...prevState,
          userToken: action.token,
          isLoading: false
        };
      default:
        return prevState;
    }
  }