anchor.diff:          item = new Listener(
             onGestureTap: (_) {
               DateTime result = new DateTime(year, month, day);
  -            if (onChanged != null)
  -              onChanged(result);
  +            onChanged(result);
             },
             child: new Container(
               height: 30.0,
  
positive.code: 
  import 'dart:async';
  
  import 'package:sky/theme/colors.dart' as colors;
  import 'package:sky/theme/typography.dart' as typography;
  import 'package:sky/widgets.dart';
  
negative.code:   DatePickerMode _mode = DatePickerMode.day;
  
    void _handleModeChanged(DatePickerMode mode) {
      userFeedback.performHapticFeedback(HapticFeedbackType_VIRTUAL_KEY);
      setState(() {
        _mode = mode;
      });
    }
  
    void _handleYearChanged(DateTime dateTime) {
      userFeedback.performHapticFeedback(HapticFeedbackType_VIRTUAL_KEY);
      setState(() {
        _mode = DatePickerMode.day;
      });
      if (onChanged != null)
        onChanged(dateTime);
    }
  
    void _handleDayChanged(DateTime dateTime) {
      userFeedback.performHapticFeedback(HapticFeedbackType_VIRTUAL_KEY);
      if (onChanged != null)
        onChanged(dateTime);
    }
  