安卓使用MQTT实现阿里云物联网云台订阅和发布主题（3）

一、订阅主题代码讲解

private final String mqtt_sub_topic = "/sys/k0wih08FdYq/LHAPP/thing/service/property/set";//订阅话题//mqtt客户端订阅主题//QoS=0时，报文最多发送一次，有可能丢失//QoS=1时，报文至少发送一次，有可能重复//QoS=2时，报文只发送一次，并且确保消息只到达一次。int[] qos = {1};String[] topic = {mqtt_sub_topic};mqttClient.subscribe(topic, qos);

二、发布主题代码讲解

private final String payloadJson = "{\"id\":%s,\"params\":{\"LightLux\": %s,\"Humidity\": %s,\"temperature\": %s},\"method\":\"thing.event.property.post\"}";private void postDeviceProperties() {try {String payload = String.format(payloadJson, String.valueOf(System.currentTimeMillis()), 10,10,10);String responseBody = payload;MqttMessage message = new MqttMessage(payload.getBytes("utf-8"));message.setQos(1);String pubTopic = "/sys/" + productKey + "/" + deviceName + "/thing/event/property/post";mqttClient.publish(pubTopic, message);Log.d(TAG, "publish topic=" + pubTopic + ",payload=" + payload);msgTextView.setText("发布成功");} catch (Exception e) {e.printStackTrace();msgTextView.setText("发布失败");Log.e(TAG, "postDeviceProperties error " + e.getMessage(), e);}}

三、回调函数代码讲解

mqttClient.setCallback(new MqttCallback() {@Overridepublic void connectionLost(Throwable cause) {//这里不需要做处理//因为在option有一个方法可以自动重连（如下）//断开后，是否自动连接,connOpts.setAutomaticReconnect(true);}@Overridepublic void deliveryComplete(IMqttDeliveryToken token) {//publish后会执行到这里System.out.println("deliveryComplete---------" + token.isComplete());}@Overridepublic void messageArrived(String topicName, MqttMessage message) throws Exception {//subscribe主题后，收到消息执行到这里try {JSONObject jsonObject = new JSONObject(message.toString());// 解析JSON数据Log.i(TAG, "消息到达,message: " + message);JSONObject paramsObject = jsonObject.getJSONObject("params");// 获取params字段中的JSONObjectint Humidity = paramsObject.getInt("Humidity");int LightLux = paramsObject.getInt("LightLux");int temperature = paramsObject.getInt("temperature");humidityTextView.setText(String.valueOf(Humidity));lightluxTextView.setText(String.valueOf(LightLux));temperatureTextView.setText(String.valueOf(temperature));} catch (JSONException e) {e.printStackTrace();}}});