title: Get current tab of DefaultTabController
body: <p>In the onPressed for my fab, I want to know the index of the tab that is currently selected in my DefaultTabController.  How do I do this?</p>
  
  <pre><code>  @override
    Widget build(BuildContext context) {
      return new MaterialApp(
        title: 'pari',
        debugShowCheckedModeBanner: false,
        theme: widget._themeData,
        home: DefaultTabController(
          length: widget._tabs.length,
          child: Scaffold(
            appBar: AppBar(
              title: Text('pari'),
              bottom: TabBar(
                isScrollable: true,
                tabs: widget._tabs,
              ),
            ),
            body: _buildBody(),
            floatingActionButton: FloatingActionButton(
                onPressed: addWagerTap,
            ),
          )
        ),
      );
    }
  </code></pre>