javascript - 在 React-Native 中切换屏幕时如何保存数据？

Question

这个问题已经有答案了:

How to use global variables in React Native? (7 个回答)

已关闭 2 年前。

在我的代码中，我有一个页面显示从数据库检索的元素列表。不过，我还添加了一个页面，允许用户选择多个过滤器。

我有两个问题:

1. 离开页面后我必须保存数据(它必须保留在那里)
2. 我必须将数据传输回元素列表。

我认为通过给过滤器屏幕一个来自前一个屏幕的变量，它可以将数据保存在那里，但它似乎不起作用。

你有什么指示我应该做什么吗？

import React from 'react'
import { SafeAreaView, View, Text } from 'react-native'
import {generalStyles} from '@gym-app/styles/general'
import { useTranslation } from 'react-i18next'
import { TouchableOpacity } from 'react-native-gesture-handler';

export default function ExerciseSelectorScreen({navigation}) {

    const {t} = useTranslation();
    var filterProps = {};

    return (
        <SafeAreaView style={generalStyles.contentContainer}>
            <View style={[generalStyles.contentContainer]}>
                <Text>{JSON.stringify(filterProps)}</Text>
                <View style={{flexDirection: 'row', justifyContent: 'space-between', alignItems: 'center'}}>
                    <Text style={generalStyles.title}>{ t('exercise.exercises') }</Text>
                    <TouchableOpacity onPress={() => {navigation.navigate('Exercises Filter', {filterProps: filterProps})}} style={{padding: 10, backgroundColor: '#ffb623'}}>
                        <Text style={{fontSize: 20, fontWeight: 'bold'}}>{t('general.filters').toUpperCase()}</Text>
                    </TouchableOpacity>
                </View>
            </View>        
        </SafeAreaView>
    )
}

import React, { useState, useEffect } from 'react'
import { View, SafeAreaView, Text, ScrollView, StyleSheet } from 'react-native'
import {generalStyles} from '@gym-app/styles/general'
import { useTranslation } from 'react-i18next'
import persistent from '@gym-app/database/persistent'
import tdb from '@gym-app/translation/object'
import CheckboxGroup from '../../components/workout/exercises/filters/CheckboxGroup'
import { useRoute } from '@react-navigation/native';

export default function ExercisesFilterScreen() {

    const {t} = useTranslation();
    const route = useRoute();
    var filterProps = route.params.filterProps;
    const [equipments, setEquipments] = useState({});
    const [selectedEquipments, setSelectedEquipments] = useState({});
    const [order, setOrder] = useState('');
    const [machine, setMachine] = useState('yes');

    useEffect(()=> {
        if (Object.values(equipments).length == 0) {
            persistent.transaction(tx => {
            tx.executeSql(
                "SELECT * FROM equipment",
                [],
                    (t, s) => {
                        var transEquip = {};
                        Object.values(s.rows._array).map((equipment) => {
                            transEquip[equipment.id] = tdb(equipment, 'name')
                        })
                        setEquipments(transEquip);
                    },
                    (t, e) => {
                        console.log(e);
                    }
                );
            });
        }
    },[equipments])

    useEffect(() => {
        filterProps.selectedEquipments = selectedEquipments;
        filterProps.order = order;
        filterProps.machine = machine;
    })

    return (
        <SafeAreaView style={{flex: 1}}>
            <ScrollView style={[generalStyles.contentContainer, {flex: 1, backgroundColor: '#ffb623'}]}>
                <Text style={{fontSize: 30, fontWeight: 'bold', color: '#ffffff', textAlign: 'center'}}>{t('general.filters').toUpperCase()}</Text>
                <View style={{marginTop: 10}}>
                <CheckboxGroup
                    title={t('exercise.availableEquipment')}
                    selected={selectedEquipments}
                    select={setSelectedEquipments}
                    multi={true}
                    options={
                        equipments
                    }
                />
                <CheckboxGroup
                    title={t('exercise.order')}
                    selected={order}
                    select={setOrder}
                    multi={false}
                    options={
                        {
                            "asc": t('exercise.easyToHard'),
                            "desc": t('exercise.hardToEasy'),
                        }
                    }
                    undefined={'allow'}
                />
                <CheckboxGroup
                    title={t('exercise.machines')}
                    selected={machine}
                    select={setMachine}
                    multi={false}
                    options={
                        {
                            "yes": t('exercise.machine.yes'),
                            "no": t('exercise.machine.no'),
                            "only": t('exercise.machine.only')
                        }
                    }
                />
                </View>
            </ScrollView>
        </SafeAreaView>
    )
}

const styles = StyleSheet.create({
    optionTitle: {
        marginBottom: 6, 
        fontSize: 24, 
        fontWeight: 'bold', 
        color: '#ffffff', 
        textAlign: 'left'
    }
})

Answer 1

使用“全局变量”的最佳方式。通过使用它，您可以在多个屏幕上访问数据并在平面列表中重新渲染。 (Redux也是解决方案，但初始很难理解)。您可以在构造函数中初始化全局变量，并可以更新屏幕中的任何位置。这是您可以了解react-native中的全局变量的链接。 https://aboutreact.com/react-native-global-scope-variables/