Pass Freezed Constructor Tear-Off to Generic Widget

Question

What the title says. I have a freezed constructor tear-off that I'm trying to pass to a Widget and it's not returning null, and I'm trying to figure out what I'm doing wrong. Here is the freezed class:

@freezed
class PatientField with SetFieldOption, _$PatientField {
  factory PatientField.firstName(String value) = PatientFirstName;
}

This is a simplified version of my initial Widget (which actually displays properly):

class SinglePatientView2 extends ConsumerWidget {
  const SinglePatientView2({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    print(PatientField.firstName('something'));
    return Theme(
        data: Theme.of(context).copyWith(dividerColor: Colors.transparent),
        child: Expanded(
            child: DefaultTabController(
                length: 1,
                child: Scaffold(
                    body: TabBarView(children: [
                  PersonTabContent<PatientField>(
                    PatientField.firstName,
                  )
                ])))));
  }
}

Then Widget that's called above looks like (simplifed version anyway):

class PersonTabContent<T> extends StatelessWidget {
  const PersonTabContent(
    this.firstNameField, {
    Key? key,
  }) : super(key: key);

  final T Function(String) firstNameField;

  @override
  Widget build(BuildContext context) {
  print(firstNameField('something'));
    return Padding(
      padding: EdgeInsets.all(doubleBySize(context, 32)),
    );
  }
}

Looking at the output, the above prints:

PatientField.firstName(value: something)
null

I don't understand why I'm getting a null value in the second Widget's build method. Any insights as to what I'm doing wrong?

score 0 · Accepted Answer · answered Apr 01 '22 at 16:17

As usual, it was my fault. For anyone stumbling onto this, the problem was my version. Constructor tear-offs have only been recently implemented, and I was still specifying dart 2.15.0 in my pubspec.yaml file. For anyone else running into this issue, check your pubspec.yaml file and ensure the top looks like the following:

name: a_new_flutter_project
description: A new Flutter project.

publish_to: 'none' 
version: 1.0.0+1

environment:
  sdk: ">=2.16.0 <3.0.0"

And that should be that.

Pass Freezed Constructor Tear-Off to Generic Widget

1 Answers1