React Native中，实时Firebase文本字段更改后，未显示新值的问题-PHP中文网问答

我正在使用React Native进行编码，并且需要从实时的Google Firebase中获取一个值。我能够获取到这个值（1），但是当数据库中的值发生变化时，我的应用程序中的文本框没有相应地变化（2）。换句话说，它与数据库的实时同步没有实现。我无法弄清楚原因。你能帮我解决这个问题吗？非常感谢！我写下的代码如下：

import React, { useState } from 'react'; import { View, Text,
TextInput} from 'react-native'; import { NavigationContainer } from
'@react-navigation/native'; import { createNativeStackNavigator } from
'@react-navigation/native-stack'; import { ImageBackground,
StyleSheet, Pressable, Image } from 'react-native'; import { Slider }
from '@react-native-assets/slider' import { Linking } from
'react-native' import database from '@react-native-firebase/database';

var Data = "";

function Room({ navigation, route }) {

//(1)   
database()
  .ref('/esp01_1/id')
  .on('value', snapshot => {
    console.log('data from firebase: ', snapshot.val());
    Data = snapshot.val()   
  });

  return (
    <View style={styles.container}>
        //(2)
        <Text style={styles.text}>{Data}</Text>
    </View>   ); }

我需要从实时的Google Firebase中获取一个值，并且当它在数据库中发生变化时，我需要它在文本框中也发生变化。

const [data, setData] = useState(); // Putting the code to load from Firebase in a useEffect call // with no dependencies (the empty array at the end) ensure it // only runs once, when the component is first rendered. useEffect(() => { database() .ref('/esp01_1/id') .on('value', snapshot => { // Calling setData puts the data in the component's state // and tells ReactJS to rerender the UI. setData(snapshot.val()); }); }, []);

全部回复(1)

P粉6708387352023-09-14 14:28:02 1楼

This is because data is loaded from Firebase (and pretty much any modern cloud API) asynchronously, and is not yet available when your <Text style={styles.text}>{Data}</Text> is executed.

You'll want to: