Question

我正在尝试在React-Native中使用现代Context API，但出现以下错误：

TypeError：TypeError：未定义不是对象（正在评估 'Context._context'）

我的createDataContext.js：

import React, { useReducer } from 'react'

export default (reducer, actions, defaultValue) => {
    const Context = React.createContext()

    const Provider = ({ children }) => {
        const [state, dispatch] = useReducer(reducer, defaultValue)

        const boundActions = {}
        for (let key in actions) {
            boundActions[key] = actions[key](dispatch)
        }

        return (
            <Context.Provider value={{ state, ...boundActions }}>
                {children}
            </Context.Provider>
        )
    }

    return { Context, Provider }
}

我的context.js：

import { AsyncStorage } from 'react-native'
import createDataContext from './createDataContext'

import { 
    LOGIN_FIRST_STEP, 
    LOGIN_SECOND_STEP,
    AUTH_MODAL, 
    SIGNIN_MODAL,
    SIGNUP_MODAL,
} from '../constants'

const INITIAL_STATE = {
    email: '',
    firstName: '',
    lastName: '',
    password: '',
    cardNumber: '',
    expiration: '', 
    CVV: '',
    billingAddress: '',
    authOpen: false,
    signupOpen: false,
    signinOpen: false,
}

const reducer = (state = INITIAL_STATE, { type, payload }) => {
    switch (type) {
        case LOGIN_FIRST_STEP: 
            const { email, firstName, lastName, password } = payload
            return {
                ...state,
                email,
                firstName,
                lastName,
                password,
            }
        case LOGIN_SECOND_STEP: 
            const { cardNumber, expiration, CVV, billingAddress } = payload
            return {
                ...state,
                email,
                cardNumber,
                expiration,
                CVV,
                billingAddress,
            }
        case AUTH_MODAL:
            return {
                ...state,
                authOpen: true,
                signupOpen: false,
                signinOpen: false,
            }
        case SIGNUP_MODAL:
            return {
                ...state,
                authOpen: false,
                signupOpen: true,
                signinOpen: false,
            }
        case SIGNIN_MODAL:
            return {
                ...state,
                authOpen: false,
                signupOpen: false,
                signinOpen: true,
            }
        default:
            return state
    }
}

const login = dispatch => values => {
    dispatch({ type: LOGIN_FIRST_STEP, payload: values })
}

const login2 = dispatch => values => {
    dispatch({ type: LOGIN_SECOND_STEP, payload: values })
}

const auth = disaptch => () => {
    dipatch({ type: AUTH_MODAL })
}

const signin = disaptch => () => {
    dipatch({ type: SIGNIN_MODAL })
}

const signup = disaptch => () => {
    dipatch({ type: SIGNUP_MODAL })
}

export const { Provider, Context } = createDataContext(
    reducer,
    { login, login2, auth, signin, signup },
    { authOpen: false , signinOpen: false, signupOpen: false }
)

package.json：

{
  "main": "node_modules/expo/AppEntry.js",
  "scripts": {
    "start": "expo start",
    "android": "expo start --android",
    "ios": "expo start --ios",
    "web": "expo start --web",
    "eject": "expo eject"
  },
  "dependencies": {
    "@apollo/react-hooks": "^3.1.1",
    "apollo-cache-inmemory": "^1.6.3",
    "apollo-client": "^2.6.4",
    "apollo-link": "^1.2.13",
    "apollo-link-error": "^1.1.12",
    "apollo-link-http": "^1.5.16",
    "apollo-link-state": "^0.4.2",
    "apollo-link-ws": "^1.0.19",
    "apollo-utilities": "^1.3.2",
    "expo": "^34.0.1",
    "formik": "^1.5.8",
    "graphql": "^14.5.6",
    "graphql-tag": "^2.10.1",
    "react": "16.8.3",
    "react-apollo": "^3.1.1",
    "react-dom": "^16.9.0",
    "react-native": "https://github.com/expo/react-native/archive/sdk-34.0.0.tar.gz",
    "react-native-gesture-handler": "~1.3.0",
    "react-native-maps": "~0.24.0",
    "react-native-reanimated": "~1.1.0",
    "react-native-web": "^0.11.4",
    "react-navigation": "^4.0.6",
    "react-navigation-stack": "^1.8.0",
    "react-navigation-tabs": "^2.5.4",
    "subscriptions-transport-ws": "^0.9.16",
    "yup": "^0.27.0"
  },
  "devDependencies": {
    "babel-preset-expo": "^6.0.0"
  },
  "private": true
}

最后是app.js：

export default App = () => {
  return (
      <ApolloProvider client={client}>
          <ApolloHooksProvider client={client}>
            <ContextProvider>
              <Root />
            </ContextProvider>
          </ApolloHooksProvider> 
      </ApolloProvider>
  )
}

当我尝试通过导入Context并使用useContext钩来使用时：

const {
    state,
    authModal
} = useContext(Context)

上述错误显示。我尝试删除react-native软件包，然后将其重新安装为最新版本。我尝试删除节点模块，清除缓存，然后重新安装它们，但似乎都无法解决问题。

Answer 1

我有同样的错误，这是因为我正在这样导入Context：

从'...'导入{Context}

代替

从“ ..”导入上下文

在React Native中使用useContext的上下文API显示TypeError

1 个答案: