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invalid_widget_preview_application

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The '@Preview(...)' annotation can only be applied to public, statically accessible constructors and functions.

Description

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The analyzer produces this diagnostic when a @Preview(...) annotation is applied to an invalid widget preview target. Widget previews can only be applied to public, statically accessible, explicitly defined constructors and functions.

Examples

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The following code produces this diagnostic because _myPrivatePreview is private:

dart
import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';

// Invalid application to private top-level function.
@Preview()
// ignore: unused_element
Widget _myPrivatePreview() => Text('Foo');

The following code produces this diagnostic because myExternalPreview is external:

dart
import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';


// Invalid application to an external function.
@Preview()
external Widget myExternalPreview();

The following code produces this diagnostic because PublicWidget._() is private:

dart
import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';

class PublicWidget extends StatelessWidget {
  // Invalid application to a private constructor.
  @Preview()
  PublicWidget._();

  @override
  Widget build(BuildContext) => Text('Foo');
}

The following code produces this diagnostic because instancePreview is an instance method:

dart
import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';

class PublicWidget extends StatelessWidget {
  // Invalid application to a instance member.
  @Preview()
  Widget instancePreview() => PublicWidget();

  @override
  Widget build(BuildContext context) => Text('Foo');
}

The following code produces this diagnostic because _PrivateWidget is private:

dart
import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';

// ignore: unused_element
class _PrivateWidget extends StatelessWidget {
  // Invalid application to a constructor of a private class.
  @Preview()
  _PrivateWidget();

  @override
  Widget build(BuildContext context) => Text('Foo');
}

The following code produces this diagnostic because _PrivateWidget is private:

dart
import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';

// ignore: unused_element
class _PrivateWidget extends StatelessWidget {
  // Invalid application to a static method of a private class.
  @Preview()
  Widget privateStatic() => _PrivateWidget();

  @override
  Widget build(BuildContext context) => Text('Foo');
}

The following code produces this diagnostic because AbstractWidget is an abstract class:

dart
import 'package:flutter/widgets.dart';
import 'package:flutter/widget_previews.dart';

abstract class AbstractWidget extends StatelessWidget {
  // Invalid application to a constructor of an abstract class.
  @Preview()
  AbstractWidget();

  @override
  Widget build(BuildContext context) => Text('Foo');
}

Common fixes

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Create a dedicated public, statically accessible, and explicitly defined constructor, top-level function, or class member for use as a preview:

Unless stated otherwise, the documentation on this site reflects Dart 3.8.1. Page last updated on 2025-05-08. View source or report an issue.