我已经在Flutter应用程序中实现了DatePicker。我试图将选择器限制为仅允许用户选择工作日。但是，我不确定如何执行此操作。我相信这与SelectableDayPredicate有关。以下是我的代码片段：

Future<Null> _selectDate(BuildContext context) async {
  final DateTime picked = await showDatePicker(
    context: context,
    initialDate: _date,
    firstDate: new DateTime(DateTime.now().year),
    lastDate: new DateTime(DateTime.now().year+1),
    // to do: I am pretty sure the SelectableDayPredicate should go somewhere here.
  );

  if (picked != null && picked != _date) {
    setState(() {
      _date = picked;
    });
  }
}

当用户点击listTile时，将调用_selectDate函数。