invalid_widget_preview_private_argument

'@Preview(...)' can only accept arguments that consist of literals and public symbols.

The analyzer produces this diagnostic when the Preview constructor is invoked with arguments that contain references to private symbols.

The following code produces this diagnostic because the constant variable _name is private to the current library:

import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';
​
const String _name = 'My Foo Preview';
​
@Preview(name: _name)
Widget myPreview() => Text('Foo');

If appropriate, the private symbol should be made public:

import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';
​
const String name = 'My Foo Preview';
​
@Preview(name: name)
Widget myPreview() => Text('Foo');

Otherwise, a different public constant symbol should be used:

import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';
​
@Preview(name: 'My Foo Preview')
Widget myPreview() => Text('Foo');