title: Call to Firebase happens only once when i open the page , then it never happens when i navigate back to it
body: <p>Am doing a call to the firebase from my ionic 4 project that gets a list of items. it only happens once I launch the app for the first time, then if I navigate to another page then back to this page. it shows a blank list. here is my code :</p>
  
  <pre><code>import { Component, OnInit } from '@angular/core';
  import { DressService, Dress } from '../services/dress.service';
  
  @Component({
    selector: 'app-list',
    templateUrl: 'list.page.html',
    styleUrls: ['list.page.scss']
  })
  export class ListPage implements OnInit {
    dress: Dress[];
    constructor(private dressService: DressService,
    ) {
      this.dressService.getDresses().subscribe(res =&gt; {
        this.dress = res;
      });
    }
  
    ngOnInit() {
  
    }
    // add back when alpha.4 is out
    // navigate(item) {
    //   this.router.navigate(['/list', JSON.stringify(item)]);
    // }
  }
  </code></pre>
  
  <p>And here is how I view the list in my <code>HTML</code> page </p>
  
  <pre><code>    &lt;ion-list&gt;
          &lt;ion-item *ngFor="let item of dress" &gt;
              &lt;img src="{{item.image_1}}"&gt;
              &lt;ion-label dir="rtl"&gt;
                  &lt;small&gt;{{item.category}}&lt;/small&gt;
                  &lt;br&gt;
                  &lt;ion-text color="secondary"&gt;
                      &lt;b&gt;{{item.title}}&lt;/b&gt;
                  &lt;/ion-text&gt;
                  &lt;br&gt;
                  &lt;ion-badge color="danger"&gt;{{item.price}} EGP&lt;/ion-badge&gt;
                  &lt;br&gt;
                  &lt;small&gt;{{item.city}}&lt;/small&gt;
              &lt;/ion-label&gt;
          &lt;/ion-item&gt;
      &lt;/ion-list&gt;
  </code></pre>