React-Native：警告：无法对卸载的组件执行React状态更新

Question

我尝试从一个屏幕转换到另一个屏幕时收到以下错误消息：

这发生在一个游戏应用程序中，游戏中涉及多个手机，并根据他们在游戏中的角色具有不同的屏幕，并取决于该手机是托管游戏还是客人。

当我尝试访问下一个屏幕时（左侧手机上），下图显示了此错误消息。左侧手机的屏幕应该与右侧的屏幕相同，但没有“下一轮”和“结束游戏”按钮。但我得到一个完全不同的屏幕与错误消息：

这是上一个屏幕的代码，用于将手机导航到此“分数”屏幕：

import React, {Component} from 'react';
import {AppRegistry, View, Text, ScrollView, StyleSheet} from 'react-native';
import {CardFlip1} from '../components/CardFlip1';
import {CardFlip2} from '../components/CardFlip2';
import colors from '../config/colors';
import {PrimaryButton} from '../components/PrimaryButton';
import AsyncStorage from '@react-native-community/async-storage';
import Orientation from 'react-native-orientation-locker';
window.navigator.userAgent = 'react-native';
import io from 'socket.io-client/dist/socket.io';

class judge_screen extends Component {
    constructor (props) {
        super(props);
        this.state = {
            game_round: '',
            player1: '',
            player2: '',
            label1: '',
            label2: '',
            current_user: ''
        }
    }

    componentWillMount = () => {
        this.getActives();
    }

    componentDidMount() {
        Orientation.lockToLandscape();
        this.socket = io("socket address is here", {
            jsonp: false
        });
    }

    getActives = async () => {
        let user = await AsyncStorage.getItem('email');
        let player_1 = await AsyncStorage.getItem('Player1');
        let player_2 = await AsyncStorage.getItem('Player2');
        let round = await AsyncStorage.getItem('Round');

        this.setState({game_round: round});
        this.setState({player1: player_1});
        this.setState({player2: player_2});
        var label_start = "Choose ";
        var label_end = "'s fate";
        var player_1_name = this.state.player1;
        var player_2_name = this.state.player2;
        var label1_str = label_start.concat(player_1_name, label_end);
        this.setState({label1: label1_str});
        var label2_str = label_start.concat(player_2_name, label_end);
        this.setState({label2: label2_str});
    }

    player1Win = async () => {
        let host = await AsyncStorage.getItem('host');
        if (host == 'yes') {
            let user = await AsyncStorage.getItem('email');
            this.setState({current_user: user});
        } else {
            let user = await AsyncStorage.getItem('users_id');
            this.setState({current_user: user});
        }
        var user_fix = this.state.current_user;
        let player_name = await AsyncStorage.getItem('Player1');
        AsyncStorage.setItem('Winner', player_name);

        fetch('fetch address is here', {
            method: 'POST',
            headers: {
            'Accept': 'application/json',
            'Content-Type': 'application.json',
            },
            body: JSON.stringify({
                email: user_fix,
                Name: player_name,
                Host: host
            })
        }).then((response) => response.json())
        .then((responseJson) => {
            if (host == 'yes') {
                this.socket.emit('end_round', 'end');
                this.props.navigation.navigate('end_round_host_screen');
            } else {
            // This is the navigation to the screen getting the error:
                this.socket.emit('end_round', 'end');
                this.props.navigation.navigate('end_round_guest_screen');
            }
        }).catch((error) => {
            console.error(error);
        });
    }

    player2Win = async () => {
        let host = await AsyncStorage.getItem('host');
        if (host == 'yes') {
            let user = await AsyncStorage.getItem('email');
            this.setState({current_user: user});
        } else {
            let user = await AsyncStorage.getItem('users_id');
            this.setState({current_user: user});
        }
        var user_fix = this.state.current_user;
        let player_name = await AsyncStorage.getItem('Player2');
        AsyncStorage.setItem('Winner', player_name);

        fetch('fetch address is here', {
            method: 'POST',
            headers: {
            'Accept': 'application/json',
            'Content-Type': 'application.json',
            },
            body: JSON.stringify({
                email: user_fix,
                Name: player_name,
                Host: host
            })
        }).then((response) => response.json())
        .then((responseJson) => {
            if (host == 'yes') {
                this.socket.emit('end_round', 'end');
                this.props.navigation.navigate('end_round_host_screen');
            } else {
            // This is the navigation to the screen getting the error:
                this.socket.emit('end_round', 'end');
                this.props.navigation.navigate('end_round_guest_screen');
            }
        }).catch((error) => {
            console.error(error);
        });
    }

    render() {
        return (
            <ScrollView>
                <View style={{flexDirection: 'row'}}>
                    <View style={styles.container}>
                        <Text style={[styles.text]}>
                            {this.state.player1}
                        </Text>
                        <CardFlip1 />
                        <PrimaryButton
                            onPress={() => this.player1Win()}
                            label={this.state.label1}
                        >
                        </PrimaryButton>
                    </View>
                    <View style={styles.container}>
                        <Text style={[styles.text]}>
                            {this.state.player2}
                        </Text>
                        <CardFlip2 />
                        <PrimaryButton
                            onPress={() => this.player2Win()}
                            label={this.state.label2}
                        >
                        </PrimaryButton>
                    </View>
                </View>
            </ScrollView>
        );
    }
}

const styles = StyleSheet.create({
    container: {
        flex: 1,
        alignItems: 'center',
        backgroundColor: colors.backgroundColor,
        margin: 10,
        paddingBottom: 5,
        borderWidth: 1,
        borderColor: colors.borderColor,
    },
    text: {
        fontSize: 18,
        color: colors.primaryText,
        marginTop: 10,
    },
    textPadding: {
        paddingBottom: 10,
    },
    headingText: {
        fontSize: 24,
        fontWeight: '500',
        color: colors.primaryText,
        margin: 10,
    },
    textMarginHorizontal: {
        marginHorizontal: 10,
    },
})

export default judge_screen;

以下是我尝试导航到的“end_round_guest_screen”的代码：

import React, {Component} from 'react';
import {View, Text, ScrollView, StyleSheet} from 'react-native';
import colors from '../config/colors';
import {PrimaryButton} from '../components/PrimaryButton';
import {ScoreBoardGuest} from '../components/ScoreBoardGuest';
import AsyncStorage from '@react-native-community/async-storage';
import Orientation from 'react-native-orientation-locker';
window.navigator.userAgent = 'react-native';
import io from 'socket.io-client/dist/socket.io';

class end_round_guest_screen extends Component {
    constructor (props) {
        super(props);
        this.state = {
            game_round: '',
            winner: ''
        }
    }

    componentWillMount = () => {
        this.getActives();
        this.getWinner();
    }

    componentDidMount() {
        Orientation.unlockAllOrientations();
        this.socket = io("socket address is here", {
            jsonp: false
        });
        this.socket.on('next_round', () => this.nextRound());
        this.socket.on('end_game', () => this.endGame());
    }

    getActives = async () => {
        let round = await AsyncStorage.getItem('Round');
        this.setState({game_round: round});
    }

    getWinner = async () => {
        let user = await AsyncStorage.getItem('users_id');
        //let host = await AsyncStorage.getItem('host');

        fetch('fetch address is here', {
            method: 'POST',
            headers: {
            'Accept': 'application/json',
            'Content-Type': 'application.json',
            },
            body: JSON.stringify({
                email: user
            })
        }).then((response) => response.json())
        .then((responseJson) => {
            this.setState({winner: responseJson});
        }).catch((error) => {
            console.error(error);
        });
    }

    nextRound = () => {
        this.props.navigation.navigate('round_start_guest_screen');
    }

    endGame = () => {
        this.props.navigation.navigate('end_game_guest_screen');
    }

    render() {
        return (
            <ScrollView>
                <View style={{alignItems: 'center'}}>
                    <Text style={styles.headingText}>
                        Round {this.state.game_round}
                    </Text>
                    <Text style={styles.text}>
                        {this.state.winner} wins this round!
                    </Text>
                </View>
                <View style={styles.container}>
                    <ScoreBoardGuest />
                </View>
            </ScrollView>
        );
    }
}

const styles = StyleSheet.create({
    container: {
        flex: 1,
        alignItems: 'center',
        backgroundColor: colors.backgroundColor,
        margin: 10,
        paddingVertical: 5,
        borderWidth: 1,
        borderColor: colors.borderColor,
    },
    text: {
        fontSize: 18,
        color: colors.primaryText,
        marginTop: 10,
    },
    headingText: {
        fontSize: 24,
        fontWeight: '500',
        color: colors.primaryText,
        margin: 10,
    },
})

export default end_round_guest_screen;

“end_round_guest_screen”显示没有加载任何状态的秒或2，然后转到带有错误消息的“Card Back”屏幕。

Answer 1

堆栈跟踪显示错误发生在end_round_guest_screen内部。根据你的描述，在导航到“卡后退”并显示错误之前它会显示2秒钟，我认为它发生在fetch回调中的this.setState({winner: responseJson})行上。

如果获取请求仍在等待响应，则会发生这种情况，然后调用nextRound或endGame处理程序，这会触发导航，从而触发卸载。当fetch获取数据并且即将调用setState时，不再安装该组件。

通常有两种方法可以解决这个问题。

1.）（反模式）使用componentDidMount / componentWillUnmount回调跟踪组件是否仍然挂载，然后在调用setState之前执行isMounted检查。

componentDidMount() {
    this.isMounted = false
}

componentWillUnmount() {
    this.isMounted = false
}

getWinner = async () => {
    //inside fetch
    if (this.isMounted) {
        this.setState({winner: responseJson})
    }
}

2.）（推荐）使用在componentWillUnmount回调中取消任何待处理的网络请求。

例如，您可以使用AbortController取消获取请求。有关示例代码，请参阅https://stackoverflow.com/a/53435967/803865。