Shows a simple way to separate logic and ui code using a `StatefulWidget` + a private `StatelessWidget`.

state_view_pattern.dart

/// 1. The public facing widget, configuration options live here
class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}
/// 2. The state / controller / bloc / view controller
/// event handlers and helper methods can live here
class _MyWidgetState extends State<MyWidget> {
  void _handlePressed() => print('todo');
  @override
  Widget build(BuildContext context) => _MyWidgetStateView(this);
}
/// 3. The stateless UI, uses `_state` to accomplish tasks, avoiding boilerplate of param passing and callbacks
///  Big blobs of layout can live here
class _MyWidgetStateView extends StatelessWidget {
  const _MyWidgetStateView(this.state, {Key? key}) : super(key: key);
  final _MyWidgetState state;
  
  @override
  Widget build(BuildContext context) => TextButton(onPressed: state._handlePressed, child: FlutterLogo());
}