title: Flutter GridView.builder how to update
body: <p>I am trying to build an Flutter App with a <code>GriView</code> of cards and I want to add a new Card every time I hit the <code>floatingActionButton</code>. But how to update my view? I know the items are added to my list, but the <code>GridView</code> doesn't show the change.</p>
  
  <pre><code>  List&lt;Widget&gt; cardsList = [];
  
    @override
    void initState() {
      super.initState();
    }
  
    @override
    Widget build(BuildContext context) {
      return new Scaffold(
        appBar: AppBar(
          title: Text('Team Kitty'),
        ),
        body: GridView.builder(
            itemCount: cardsList.length,
            gridDelegate:
                SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 3),
            itemBuilder: (BuildContext context, int index) {
              return Container(child: cardsList[index]);
            }),
        floatingActionButton: new FloatingActionButton(
          onPressed: addCard(),
          tooltip: 'Add Card',
          child: new Icon(Icons.add),
        ),
      );
    }
    addCard() {
      setState(() {
        cardsList.add(_RobotCard());
      });
    }
  }
  </code></pre>
  
  <p>I find it hard to find good Grid documentation, maybe someone has a hint?</p>
  
  <p>Thx Guys</p>