Future<Uint8List> toImage(BuildContext context, Size size) async {
  final devicePixelRatio = MediaQuery.of(context).devicePixelRatio;
  final recorder = ui.PictureRecorder();
  final canvas = Canvas(recorder);

  // Масштабируем канвас под плотность пикселей
  canvas.scale(devicePixelRatio);

  final painter = MyPainter(); // <-- ваш кастомный painter
  painter.paint(canvas, size);

  // Считаем итоговый размер
  final width = (size.width * devicePixelRatio).floor();
  final height = (size.height * devicePixelRatio).floor();

  // Получаем изображение
  final imageResult = await recorder
      .endRecording()
      .toImage(width, height);

  // Конвертируем в PNG
  final byteData = await imageResult.toByteData(
    format: ui.ImageByteFormat.png,
  );

  return byteData!.buffer.asUint8List();
}

class AppSpacer extends StatelessWidget {
  final double? width;
  final double? height;

  const AppSpacer._({Key? key, this.width, this.height}) : super(key: key);

  factory AppSpacer.p32() => const AppSpacer._(height: 32, width: 32);
  factory AppSpacer.p24() => const AppSpacer._(height: 24, width: 24);
  factory AppSpacer.p16() => const AppSpacer._(height: 16, width: 16);
  factory AppSpacer.p8()  => const AppSpacer._(height: 8, width: 8);

  @override
  Widget build(BuildContext context) {
    return SizedBox(width: width, height: height);
  }
}

import 'package:url_launcher/url_launcher.dart';

Future<void> openSettings() async {
  Uri url;
  if (defaultTargetPlatform == TargetPlatform.iOS) {
    url = Uri.parse('app-settings:');
  } else if (defaultTargetPlatform == TargetPlatform.android) {
    url = Uri.parse('package:uly.vlog.diary');
  } else {
    throw Exception('Unsupported platform');
  }

  if (await canLaunchUrl(url)) {
    await launchUrl(url);
  } else {
    throw 'Could not launch $url';
  }
}

import 'package:permission_handler/permission_handler.dart';

openAppSettings();

ListView.builder(
  itemCount: items.length,
  itemExtent: 72, // фиксированная высота в пикселях
  itemBuilder: (_, i) => ItemTile(item: items[i]),
);

ListView.builder(
  itemCount: items.length,
  prototypeItem: const ItemTile(item: sampleItem),
  itemBuilder: (_, i) => ItemTile(item: items[i]),
);