title: Flutter ListView not updating
body: <p>I wanted to create a ListView in Flutter that update when new data arrives. I am using a RefreshIndicator that triggers the list loading for testing. For my list I am using a ListBuilder to map my objects to view objects.</p>
  
  <p>From what I understand, the setState() should trigger an update to my list, however it does not.</p>
  
  <p>Debugging showed that my _listContent is actually filled with 72 items after when the setState() callback is called. Why does my list not auto update? Am I missing something?</p>
  
  <pre><code>class MyHomePage extends StatefulWidget {
    MyHomePage({Key key, this.title}) : super(key: key);
  
    final String title;
  
    @override
    _MyHomePageState createState() =&gt; new _MyHomePageState();
  }
  
  class _MyHomePageState extends State&lt;MyHomePage&gt; {
    @override
    Widget build(BuildContext context) {
      List&lt;Manga&gt; _listContent = new List&lt;Manga&gt;();
  
      void _addMangas(List&lt;Manga&gt; mangas) {
        setState(() {
          _listContent.addAll(mangas);
          print('Cleared list');
          });
      }
  
      Future&lt;Null&gt; _onRefresh() {
        Completer&lt;Null&gt; completer = new Completer&lt;Null&gt;();
  
        loadMangaItems().then((mangas) =&gt; _addMangas(mangas));
        completer.complete();
  
        return completer.future;
      }
  
      return new Scaffold(
        appBar: new AppBar(
  
          title: new Text(widget.title),
        ),
        body: new RefreshIndicator(
            child: new ListView.builder(
                itemCount: _listContent.length,
                itemBuilder: (BuildContext ctx, int index) {
                  Manga manga = _listContent[index];
                  return new MangaItem(
                    name: manga.writtenName,
                    number: manga.currentNr,
                    state: false,
                  );
                }),
            onRefresh: _onRefresh),
         );
      }
  }
  </code></pre>