ngx-chart: Show live data, angular 4.3

Question

i want to visualize some live data in the ngx-chart-gauge.
I build this up with this demo: https://swimlane.gitbooks.io/ngx-charts/content/v/6.0.2/charts/gauge.html
I get my livedata from a Service and want to show the data in the ngx-chart-gauge. I get the data from the Service ClassdataproviderService, which saves the objects in the array 'single'.
This is my ngx-chart-gauge component:

import {Component, OnInit, OnChanges, AfterViewInit, AfterViewChecked, AfterContentChecked, AfterContentInit, NgModule} from '@angular/core';
import {NgxChartsModule} from '@swimlane/ngx-charts';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import {BrowserModule} from '@angular/platform-browser';
import {TempdatagiaService} from '../paho/tempdatagia.service';
import {ClassdataproviderService} from '../mqtt/classdataprovider.service';
import * as d3 from 'd3';

@Component({
  selector: 'app-mqtt',
  templateUrl: './mqtt.component.html',
  styleUrls: ['./mqtt.component.css']
})
export class MqttComponent implements OnChanges {

  view: any[] = [700, 400];
  data: any[];
  multi: any[];
  autoScale = true;

  constructor(private classdataproviderServie: ClassdataproviderService) {
  }


  ngOnChanges() {

      this.data = this.classdataproviderServie.single;

  }



  colorScheme = {
    domain: ['#5AA454', '#A10A28', '#C7B42C']
  };

  onSelect(event) {
    console.log(event);
  }
}

This ist the ngx-chart-gauge.html

<ngx-charts-gauge
  [view]="view"
  [scheme]="colorScheme"
  [results]="data"
  [min]="0"
  [max]="100"
  [angleSpan]="240"
  [startAngle]="-120"
  [units]="'Temperature'"
  [bigSegments]="10"
  [smallSegments]="5"
  (select)="onSelect($event)">
</ngx-charts-gauge>

And this is my Service, where i get the data from:

import { Injectable } from '@angular/core';
import { Component, OnInit } from '@angular/core';
import {Paho} from '../../../node_modules/ng2-mqtt/mqttws31';




@Injectable()
export class ClassdataproviderService {

  public name: string;
  public value: string;

  single = [
    {
      name: '1',
      value: '15'
    },
    {
      name: '2',
      value: '20'
    }/*,
    {
      name: '3',
      value: '73'
    }*/
  ];



// Create a client instance
  client: any;
  packet: any;

  constructor() {



    // this.client = new Paho.MQTT.Client('broker.mqttdashboard.com', 8000,  'clientId-FUp9rr6sZS');
    this.client = new Paho.MQTT.Client('wpsdemo.gia.rwth-aachen.de', 8080, 'Steffen');

    this.onMessage();
    this.onConnectionLost();
    // connect the client
    this.client.connect({onSuccess: this.onConnected.bind(this)});
  }

  // called when the client connects
  onConnected() {
    console.log('Connected');
    this.client.subscribe('node/m1/temperature');
    //this.sendMessage('HelloWorld');
  }

  sendMessage(message: string) {
    const packet = new Paho.MQTT.Message(message);
    packet.destinationName = 'node/m1/temperature';
    this.client.send(packet);
  }

  // called when a message arrives
  onMessage() {
    this.client.onMessageArrived = (message: Paho.MQTT.Message) => {
      console.log('Message arrived : ' + message.payloadString);
      this.single.push({name: 'test', value: message.payloadString});
      console.log(this.single);
    };
  }

  // called when the client loses its connection
  onConnectionLost() {
    this.client.onConnectionLost = (responseObject: Object) => {
      console.log('Connection lost : ' + JSON.stringify(responseObject));
    };
  }

When i try to inject the data in the gauge with OnInit, the gauge is not updating. To solve this i tried OnChanges, but now i get the ERROR TypeError: Cannot read property 'big' of undefined...
I dont know if its possible to auto update the gauge automatically without OnChanges or how to avoid the ERR with the OnChanges lifecycle hook?

Answer 1

Now i tried out many solutions and the most effective is by using an observable, to observe my Service where i get the data from. The Service, which injects the data in the ngx-chart-component, withe the observable, looks like:

import { Injectable } from '@angular/core';
import { Component, OnInit } from '@angular/core';
import {Paho} from '../../../node_modules/ng2-mqtt/mqttws31';
import 'rxjs/add/observable/interval';
import {AddDataService} from './datawindow/addmqtt/formmqtt/addmqtt.service';

@Injectable()
export class ClassdataproviderService {
  public name: string;
  public value: string;

  single = [
    {
      name: '',
      value: ''
    }
  ];

// Create a client instance
  client: any;
  packet: any;

  constructor() {

   this.addDataService.componentMethodCalled$.subscribe(
  () => {
    this.client = new Paho.MQTT.Client('wpsdemo.gia.rwth-aachen.de', 8080, 'Steffen');
    this.onMessage();
    this.onConnectionLost();
    // connect the client
    this.client.connect({onSuccess: this.onConnected.bind(this)});
  }}

  // called when the client connects
  onConnected() {
    console.log('Connected');
    this.client.subscribe('node/m1/temperature');
    //this.sendMessage('HelloWorld');
  }

  sendMessage(message: string) {
    const packet = new Paho.MQTT.Message(message);
    packet.destinationName = 'node/m1/temperature';
    this.client.send(packet);
  }

  // called when a message arrives
  onMessage() {
    this.client.onMessageArrived = (message: Paho.MQTT.Message) => {
      console.log('Message arrived : ' + message.payloadString);
      this.single.push({name: 'test', value: message.payloadString});
      console.log(this.single);
    };
  }

  // called when the client loses its connection
  onConnectionLost() {
    this.client.onConnectionLost = (responseObject: Object) => {
      console.log('Connection lost : ' + JSON.stringify(responseObject));
    };
  }

Now the single array will be updatetd every time i get new data and it works perfectly with ngx-charts. And use ngOnInit as lifecyclehook in the gauge-component.