title: Angular 2 - NgFor not updating view
body: <p>I am working on angular 2 project and I am having an issue when I am trying to change the list . NgFor not recognizing the changes , and displaying only the list loaded at first time .</p>
  
  <p>here is an example code when I am loading all list and imminently after loading I reset it with null . the view still displaying all the list ...</p>
  
  <p>this is my component constructor for example :</p>
  
  <pre><code> constructor( private songService : SongService)
      this.songService.getSongs()
           .subscribe(songsList =&gt; {
               this.songs = songsList;
           });
  
      this.songs = null;
  
  }
  </code></pre>
  
  <p>and this is the html :</p>
  
  <pre><code>&lt;div class="row"&gt;
      &lt;div  *ngFor= "let song of songs" class="col-md-4"&gt;
       &lt;app-song-item [song]="song"&gt;&lt;/app-song-item&gt;
      &lt;br&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>