Enzo Lizama Error handling in Flutter @enzoftware 

KotlinConf 2019: Error Handling Strategies for Kotlin Programs by Nat Pryce & Duncan McGregor What is failure? 

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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 

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. 

https://flutter.dev/docs/testing/errors How Flutter handle errors 

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FlutterError.onError = (FlutterErrorDetails details) { FlutterError.dumpErrorToConsole(details); if (kReleaseMode) { exit(1); // Report problem and track it } }; 

/// 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 } } 

/// 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 } } 

An example of error handling in Flutter A strategy 

class Failure { final String message; final int statusCode; Failure(this.message, this.statusCode); @override String toString() => "Error $statusCode. $message."; } 

Future> 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); } } 

Future> 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); } } 

void retrieveHotels() async { try { _hotels = await repository.fetchHotels(); } on Failure catch (e) { _failure = e; } notifyListeners(); } 

if (hotelBloc.failure != null) { return Center(child: Text(hotelBloc.failure.toString())); } ... // The other widgets 

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 

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