推荐开源项目：React Native Mqtt - 轻松集成 MQTT 协议到你的React Native应用

import React, { useEffect } from 'react';
import { View, Text } from 'react-native';
import mqtt from 'react-native-mqtt';
 
const options = {
  host: 'mqtt://broker.hivemq.com',
  port: 8000,
  clientId: 'mqtt-react-native-client-id',
  username: 'your_username', // optional
  password: 'your_password', // optional
};
 
const MqttComponent = () => {
  useEffect(() => {
    const client = mqtt.connect(options);
 
    client.on('connect', () => {
      console.log('Connected to MQTT server');
      client.subscribe('your/topic');
    });
 
    client.on('message', (topic, message) => {
      console.log(`Received message on ${topic}: ${message.toString()}`);
      // 处理接收到的消息
    });
 
    return () => {
      // 清理操作，比如断开连接
      client.end();
    };
  }, []);
 
  return (
    <View>
      <Text>MQTT Client connected</Text>
    </View>
  );
};
 
export default MqttComponent;

这个代码示例展示了如何在React Native应用中使用react-native-mqtt库来连接MQTT服务器，订阅一个主题，并接收消息。这个例子使用了React Native的函数组件和Hooks API，并在组件挂载时建立MQTT连接，在卸载时清理资源。