Question

AMQJS0005E内部错误。错误消息：无法读取属性＆＃39;订阅＆＃39;未定义的

我在我的应用程序中包含了eclipse paho javascript客户端库。连接已建立，但我无法订阅主题。这是我用过的代码..

＆＃13;

import { Component } from '@angular/core';
import { NavController, NavParams ,MenuController } from 'ionic-angular';
import { Setuser } from '../../providers/setuser';
import { Platform } from 'ionic-angular';
import { Paho} from 'ng2-mqtt/mqttws31';
/*
  Generated class for the Usershome page.

  See http://ionicframework.com/docs/v2/components/#navigation for more info on
  Ionic pages and navigation.
*/
@Component({
  selector: 'page-usershome',
  templateUrl: 'usershome.html'
})
export class UsershomePage {
  client :any;
  message :any;

  constructor(public navCtrl: NavController, public navParams: NavParams,public menu:MenuController,public setUserProvider: Setuser,public platform:Platform) {
  	this.menu.open(); 
    
  }
  

  ionViewDidLoad() {
   this.menu.enable(true);
    console.log('ionViewDidLoad UsershomePage');
  }
  exitApp(){
  console.log("----------");
  this.platform.exitApp();
  }
  connectToMqtt(){
  this.client = new Paho.MQTT.Client("test.mosquitto.org",8080,"abc");

// set callback handlers
this.client.onConnectionLost = this.onConnectionLost;
this.client.onMessageArrived = this.onMessageArrived;

// connect the client
this.client.connect({onSuccess:this.onConnect});
}

// called when the client connects
 onConnect() {
  // Once a connection has been made, make a subscription and send a message.
  console.log("onConnect");
  this.client.subscribe("mitsuruog");
  this.message = new Paho.MQTT.Message("Hello");
  this.message.destinationName = "World";
  this.client.send(this.message);
}

// called when the client loses its connection
 onConnectionLost(responseObject) {
  if (responseObject.errorCode !== 0) {
    console.log("onConnectionLost:"+responseObject.errorMessage);
  }
}

// called when a message arrives
 onMessageArrived(message) {
  console.log("onMessageArrived:"+message.payloadString);
}
  
  

 

}

＆＃13;

Answer 1

通过修改行

可以解决您的直接问题

this.client.connect({onSuccess:this.onConnect.bind(this)});

或者，令您惊讶的是，删除this.和client引用前面的所有message。

您应该了解JavaScript中this的确切含义。与Java或C＃不同。要了解删除的原因，请了解闭包和箭头函数。

良好的起点（您的问题实际上可能被标记为此问题的副本）： How to access the correct `this` context inside a callback?

paho mqtt javascript客户端无法订阅主题

1 个答案: