Question

我正在尝试使用上下文API更新我的react native应用程序的主题，但是它抛出错误setThemeMode不是一个函数。（在'setThemeMode（themeMode ==='light'？'dark'：'light'）'中，'setThemeMode'为“ i”）

我参考了以下博客文章 https://www.smashingmagazine.com/2020/01/introduction-react-context-api/

Main Error Image

ThemeContext.js

import React from 'react';

const ThemeContext = React.createContext(['light', () => {}]);
export default ThemeContext;

App.js

    import React, {useState} from 'react';

    import Nav from './src/navigation/Nav';
    import 'react-native-gesture-handler';
    import ThemeContext from './src/context/ThemeContext';

    const App = () => {
    const [theme] = useState("light");
    return (
    <>
    <ThemeContext.Provider value={theme}>
        <Nav />
    </ThemeContext.Provider>
    </>
    );
    };

    export default App;

Settings.js

    import React, {useContext} from 'react';
    import {View, Text, TouchableHighlight, Alert} from 'react-native';
    import Icon from 'react-native-vector-icons/dist/Ionicons';

    import Switches from 'react-native-switches';

    import ThemeContext from './../context/ThemeContext';
    import AppTheme from './../Colors';

    import {
    widthPercentageToDP as wp,
    heightPercentageToDP as hp,
    } from 'react-native-responsive-screen';
    import ThemeSwitch from './ThemeSwitch';

    const Settings = () => {
    const [themeMode, setThemeMode] = useContext(ThemeContext);
    const theme = useContext(ThemeContext);
    const currentTheme = AppTheme[theme];

    return (
        <>
    <TouchableHighlight
        onPress={() => setThemeMode(themeMode === 'light' ? 'dark' : 'light')} 
        style={{
            backgroundColor: 'black',
            borderRadius: 100,
            width: wp(14),
            height: wp(14),
            justifyContent: 'center',
            alignItems: 'center',
        }}>
        <Icon name="md-arrow-round-back" size={wp(8)} color="white" />
        </TouchableHighlight>
    </>
    );
    };

    export default Settings;

Nav.js

    import React from 'react';
    import {NavigationContainer} from '@react-navigation/native';
    import {createStackNavigator} from '@react-navigation/stack';

    import Welcome from './../components/Welcome';
    import Settings from './../components/Settings';
    import Main from './../components/Main';

    const Stack = createStackNavigator();

    const Nav = () => {
    return (
        <NavigationContainer>
        <Stack.Navigator
            screenOptions={{
            headerShown: false,
            }}>
            <Stack.Screen name="Main" component={Main} />
            <Stack.Screen name="Settings" component={Settings} />
            <Stack.Screen name="Welcome" component={Welcome} />
        </Stack.Navigator>
        </NavigationContainer>
    );
    };

    export default Nav;

Colors.js

        const AppTheme = {
    light: {
        name: 'light',
        textColor: 'black',
        backgroundColor: 'white',
    },
    dark: {
        name: 'dark',
        textColor: 'white',
        backgroundColor: 'black',
    },
    };

    export default AppTheme;

我想动态更新上下文。请原谅我如此愚蠢的错误，但我是新来的回应者，Js。我已附上问题图片。我认为 useContext 出了点问题，因为当我尝试 console.log（ThemeContext）时，它显示的是 undefined 而不是光。

Answer 1

const [themeMode, setThemeMode] = useContext(ThemeContext);

应该是

const [themeMode, setThemeMode] = useState(ThemeContext);

在React Native钩子中动态更新上下文

1 个答案: