Error handling in Flutter

Transcript

1. Enzo Lizama Error handling in Flutter @enzoftware
2. KotlinConf 2019: Error Handling Strategies for Kotlin Programs by Nat Pryce & Duncan McGregor What is failure?
4. Programs can go wrong for so many reasons • Invalid input ◦ Strings with invalid values ◦ Numbers out of range ◦ Unexpectedly null pointers exceptions • External failure ◦ File not found ◦ Timeouts • Programming errors ◦ Array out of bound ◦ Invalid state • System error ◦ Out of memory
5. https://dart.dev/guides/libraries/library-tour#exceptions Exceptions are considered conditions that you can plan ahead for and catch. Errors are conditions that you don’t expect or plan for.
6. https://flutter.dev/docs/testing/errors How Flutter handle errors
8. FlutterError.onError = (FlutterErrorDetails details) { FlutterError.dumpErrorToConsole(details); if (kReleaseMode) { exit(1); // Report problem and track it } };
9. /// This is an [FlutterErrorDetails], appears instead of the red screen /// to avoid scare the users ErrorWidget.builder = (FlutterErrorDetails details) => CustomErrorWidget(); ... class CustomErrorWidget extends StatelessWidget { @override Widget build(BuildContext context) { // Your custom error widget } }
10. /// This is an [FlutterErrorDetails], appears instead of the red screen /// to avoid scare the users ErrorWidget.builder = (FlutterErrorDetails details) => CustomErrorWidget(); ... class CustomErrorWidget extends StatelessWidget { @override Widget build(BuildContext context) { // Your custom error widget } }
11. An example of error handling in Flutter A strategy
12. class Failure { final String message; final int statusCode; Failure(this.message, this.statusCode); @override String toString() => "Error $statusCode. $message."; }
13. Future<List<HotelModel>> getHotels() async { try { final data = await http.get(_baseUrl + _endPoint); final responseList = json.decode(data.body); return [for (final hotel in responseList) HotelModel.fromJson(hotel)]; } on SocketException { throw Failure("No internet connection", 400); } on HttpException { throw Failure("Not found request", 404); } on FormatException { throw Failure("Invalid JSON format", 666); } catch (e) { throw Failure("Unknown error", 888); } }
14. Future<List<HotelModel>> getHotels() async { try { final data = await http.get(_baseUrl + _endPoint); final responseList = json.decode(data.body); return [for (final hotel in responseList) HotelModel.fromJson(hotel)]; } on SocketException { throw Failure("No internet connection", 400); } on HttpException { throw Failure("Not found request", 404); } on FormatException { throw Failure("Invalid JSON format", 666); } catch (e) { throw Failure("Unknown error", 888); } }
15. void retrieveHotels() async { try { _hotels = await repository.fetchHotels(); } on Failure catch (e) { _failure = e; } notifyListeners(); }
16. if (hotelBloc.failure != null) { return Center(child: Text(hotelBloc.failure.toString())); } ... // The other widgets
17. Catcher Catcher is Flutter plugin which automatically catches error/exceptions and handle them. Catcher offers mutliple way to handle errors https://pub.dev/packages/catcher
18. Enzo Lizama • https://github.com/enzoftware/hotel_booking_app • https://www.youtube.com/watch?v=pvYAQNT4o0I • https://flutter.dev/docs/testing/errors Utils resources Thanks! @enzoftware