anchor.diff:        case DatePickerMode.day:
           picker = new MonthPicker(
             selectedDate: selectedDate,
  -          onChanged: onChanged,
  +          onChanged: _handleDayChanged,
             firstDate: firstDate,
             lastDate: lastDate,
             itemExtent: _calendarHeight
  
positive.code:         item = new Listener(
            onGestureTap: (_) {
              DateTime result = new DateTime(year, month, day);
              if (onChanged != null)
                onChanged(result);
            },
            child: new Container(
              height: 30.0,
  
negative.code:     this.lastDate
    }) : super(itemExtent: 50.0) {
      assert(selectedDate != null);
      assert(onChanged != null);
      assert(lastDate.isAfter(firstDate));
    }
    DateTime selectedDate;
  