title: TabBar setting setting state of tabviews
body: <p>I have a Main page with a tabbar with 5 tabs. In Main page, i load a JSON from internet and set different parts of it in each tab. It's a world cup app, showing a tab for each match fase (groups, round of 16, quarterfinals, semifinal, and final). When each tab is loaded, i get the json and build a list view.</p>
  
  <p>In additional, i want to set a button to reload the information (something like a fab or action in appbar). But, when i reload the JSON, how do i setstate of the actual tab?</p>
  
  <p>This is my Main page widget build:</p>
  
  <pre><code>Widget build(BuildContext context) {
  return new Scaffold(
    appBar: new AppBar(
      leading: new IconButton(
        icon: new Icon(Icons.arrow_back),
        onPressed: () =&gt; Navigator.pop(context),
      ),
      title: new Text(title),
    ),
    body: new Center(
      child: new TabBarView(
        controller: _tabController,
        children: &lt;Widget&gt;[
          new GroupStageMatches(),
          new RoundOfSixteen(),
          new QuarterFinals(),
          new SemiFinal(),
          new Final(),
        ],
      ),
    ),
    bottomNavigationBar: new Material(
      color: Colors.blueAccent,
      child: new TabBar(
        controller: _tabController,
        tabs: &lt;Widget&gt;[
          new Tab(text: "Grupos"),
          new Tab(text: "Oitavas"),
          new Tab(text: "Quartas"),
          new Tab(text: "Semi"),
          new Tab(text:"Final"),
        ],
      ),
    ),
    floatingActionButton: new FloatingActionButton(
      onPressed: () {
        setState(() {
          sing.updateData();
        });
      }
    ),
  );}
  </code></pre>