dashboard.dart

class Dashboard extends StatefulWidget {
  Dashboard({Key key}) : super(key: key);

  @override
  _DashboardState createState() => new _DashboardState();
}
class _DashboardState extends State<Dashboard> {
  
  ...
  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
        length: _currentCategory == 3 ? 1 : 3,
        child: PlatformParent(
          children: PlatformContent(),
          ...
        ));
  }
}