Named parameters can't start with an underscore on null safe flutter

Question

I am not sure why this fails? How can this be fixed?

As per this https://dart.dev/tools/diagnostic-messages#private_optional_parameter it's being told to make them without underscores. But that makes the variable public instead of being a private?

class ContactElement extends StatelessWidget {


  final IconData _icon;
  final String _heading;
  final String _describer;

  const ContactElement({
    Key? key,
    required this._icon,
    required this._heading,
    required this._describer,
  }) : super(key: key);
}

please help

`final IconData _icon; final String _heading; final String _describer; ContactElement({IconData icon, String heading, String describer}) : _icon = icon, _heading = heading, _describer = describer;` — pskink, Oct 03 '21 at 05:35

score 9 · Accepted Answer · edited Aug 13 '22 at 14:29

9

Got this answer in comments from @pskink. Posting it here

final IconData _icon;
final String _heading;
final String _describer;

ContactElement({
  IconData icon,
  String heading,
  String describer,
}) : _icon = icon, _heading = heading, _describer = describer;

edited Aug 13 '22 at 14:29

barracus

368
5
15

answered Oct 14 '21 at 20:34

This needs to extend the super class `super()` of `StatelessWidget` ([Dart explanation](https://dart.dev/guides/language/language-tour#extending-a-class), look at my answer – Guillem Puche Mar 09 '22 at 16:38

score 4 · Answer 2 · answered Mar 09 '22 at 16:34

Underscore means a private field for Dart (more here)

class ContactElement extends StatelessWidget {
  const ContactElement({
    Key? key,
    required IconData icon,
    required String heading,
    required String describer,
  }) : _icon = icon,
       _heading = heading,
       _describer = describer,
       super(key: key);
  
  // Private fields
  final IconData _icon;
  final String _heading;
  final String _describer;

  // If you want that other parts of the code could to these
  // fields, use getters and setters. Here is a getter example. 
  IconData get icon => _icon;
  ...
}

Amir Hossein Rahmanzadeh · Answer 3 · 2021-10-03T05:35:27.703

-1

This is not possible since if you define a constructor for private variables you can not instantiate the class outside it's file since the variables are private, so the alternative is:

 class ContactElement extends StatelessWidget {
   late IconData _icon;
   late  String _heading;
   late String _describer;

  ContactElement( {required IconData icon, required String heading, describer}) {
    _icon = icon;
    _heading = heading;
    _describer = describer;
  }
}

edited Oct 03 '21 at 05:35

answered Oct 03 '21 at 04:08

Amir Hossein Rahmanzadeh

402
1
11

Just tested it does not seems to work. – Oct 03 '21 at 05:08
@LatheeshVMVilla The answer updated just needed minor refactors, I checked it and it works. – Amir Hossein Rahmanzadeh Oct 03 '21 at 05:36
You should prefer using [an initializer list](https://stackoverflow.com/a/64548861/) instead. – jamesdlin Oct 03 '21 at 05:50
`late` variables don't initialize on constructors, I think – Guillem Puche Mar 09 '22 at 16:41
`late` variables don't initialize on constructors, I think. You also need to extend the super class `super()` of `StatelessWidget` ([Dart explanation](https://dart.dev/guides/language/language-tour#extending-a-class)), look at [my answer](https://stackoverflow.com/a/71412824/9192954) – Guillem Puche Mar 09 '22 at 16:43

Named parameters can't start with an underscore on null safe flutter

3 Answers3

Linked