Can't find class 'PreviewProvider'

[Misaka-Tang]

I try to download and use this extension but it doesn't work. System can't find superclass, here're my codes

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Namer App',
      theme: ThemeData(
        useMaterial3: true,
        colorScheme: ColorScheme.fromSwatch(
          primarySwatch: Colors.blue,
        ).copyWith(secondary: Colors.red),
      ),
      home: Dashboard()
      
    );
  }
}



class WidgetPreview extends PreviewProvider {
 @override
 List<Preview> get previews { 
  return [
     Preview( 
       child: 
     ),
   
  ];
 }
}

and there's no icon to preview.