Flutter/Dart：从 Switch/Case 返回值

Question

I am trying to build a date validator in my flutter application, using a switch case:

Link to DartPad sample

class DateValidator {
  DateValidator({this.selectedDate, this.type});
  final String type;
  final DateTime selectedDate;


  dateValidator() {
    String _errorMsg = '';
    switch (type) {
      case "event":
        {
          if (selectedDate == null) _errorMsg = "No date selected";
          if (selectedDate == DateTime.now())
            _errorMsg = "Check your selected date";
        }
        break;

      case "test2":
        {
          print("test2");
        }
        break;

      default:
        {
          print("Invalid Date");
        }
        break;
    }

    return _errorMsg;
  }
}

void main() {
  DateValidator(
    selectedDate: DateTime.now(),
    type: 'event',
  ).dateValidator().then((value) {
    print(value);
  });
}

I would like to then return _errorMsg like so:

DateValidator(type: widget.deal.date).dateValidator()
.then((errorMsg){
  print(errorMsg);
});

This results in:

Class 'bool' has no instance method 'then'.

How can I correctly return the value?

Answer 1

Replace your:

dateValidator() {

With:

Future<String> dateValidator() async {

Reason to do this: If you want to get your result in then method then you need to specify your method's return type as Future<String> because then is a method defined in Future class.