upstream-flutter-samples/cupertino_gallery/lib/widgets/sheet_page.dart

import 'package:flutter/cupertino.dart';

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

  @override
  Widget build(BuildContext context) {
    return CupertinoPageScaffold(
      navigationBar: const CupertinoNavigationBar(middle: Text('Sheet')),
      child: Center(
        child: CupertinoButton.filled(
          child: const Text('Show Sheet'),
          onPressed: () {
            Navigator.of(context).push(
              CupertinoSheetRoute<void>(
                scrollableBuilder:
                    (context, controller) {
                      return CupertinoPageScaffold(
                        navigationBar: CupertinoNavigationBar(
                          middle: const Text('Sheet'),
                          trailing: GestureDetector(
                            child: const Icon(CupertinoIcons.xmark),
                            onTap: () {
                              Navigator.of(context).pop();
                            },
                          ),
                        ),
                        child: const Center(child: Text('This is a sheet')),
                      );
                    },
              ),
            );
          },
        ),
      ),
    );
  }
}