Inside main.dart I am using the 2 callbacks for handling exceptions caught by flutter and not caught by flutter as follows:
void main() async {
MyErrorsHandler.initialize();
FlutterError.onError = (details) async {
FlutterError.presentError(details);
MyErrorsHandler.onErrorDetails(details);
};
PlatformDispatcher.instance.onError = (error, stack){
MyErrorsHandler.onError(error, stack);
return true;
};
runApp(const ProviderScope(child: MyApp()));
}
But when I throw exceptions myself like when making an HTTP request:
static Future<BasketViewDto> getAsync(String basketId) async {
final url = Uri.parse('${ApiConfigurations.BaseUrl}/Baskets/$basketId');
final response = await http.get(url);
if (response.statusCode == 200) {
final result = json.decode(response.body)['result'];
final BasketViewDto basket = BasketViewDto.fromJson(result);
return basket;
} else {
throw Exception("Failed to get Basket");
}
}
OnError does not catch that exception. So how can I define a global place where I can handle(log) all exceptions that I throw in any place inside my code?
Related
I encountered a warning while working with the Carousel Slider library I checked but could not find the cause Thank you for helping me find my problem
I put the classes that could have caused this warning here and below
Thank you all
import 'package:http/http.dart' as http;
import 'package:multi_shop/model/carousel.dart';
class RemoteService {
static var client = http.Client();
static Future<dynamic> fetchCarouselData() async {
try{
final response = await client.get(
Uri.parse('https://my-shop.com/home-carousels'),
);
if(response.statusCode == 200){
return carouselFromJson(response.body);
}
return null;
} catch(e){
return null;
}
}
}
import 'package:get/get.dart';
import 'package:get_storage/get_storage.dart';
import 'package:multi_shop/http/remote_services.dart';
import 'package:multi_shop/model/carousel.dart';
class HomeController extends GetxController{
var box = GetStorage();
var isLoading = false;
List<Carousel> carouselData = [];
#override
void onInit() {
fetchCarousel();
if(box.read('carouselData') != null) {
carouselData.assignAll(box.read('carouselData'));
}
super.onInit();
}
void fetchCarousel() async {
try{
isLoading = true;
update();
List<Carousel> data = await RemoteService.fetchCarouselData();
carouselData.assignAll(data);
box.write('carouselData', data);
}finally{
isLoading = false;
update();
print('data fetch done');
}
}
}
Your code is not type safety,
do not use dynamic if you already have Carousel type;
return empty array instead of null;
I would refactor your code as
static Future<List<Carousel>> fetchCarouselData() async {
try{
final response = await client.get(
Uri.parse('https://my-shop.com/home-carousels'),
);
if(response.statusCode == 200){
return carouselFromJson(response.body);
}
return [];
} catch(e){
return [];
}
}
And please, do not call async code inside onInit(), use onReady() for async stuff, read comments of these methods for more.
For more enhancement I would recommend use fluent_result to deal better with exceptions and errors in the code.
main() async {
try {
final t = Test();
await Future.delayed(Duration(seconds: 1));
} catch (e) {
// Never printed
print("caught");
}
}
void willThrow() async {
throw "error";
}
class Test {
Test() {
willThrow();
}
}
If the "async" keyword is removed from willThrow everything works as expected.
Is it because you can't await a constructor? If so is there anyway to catch async errors in a constructor body?
Have this a go:
void main() async {
try {
final t = Test();
await Future.delayed(Duration(seconds: 1));
} catch (e) {
// Never printed
print("caught");
}
}
Future<void> willThrow() async {
throw "error";
}
class Test {
Test() {
willThrow().catchError((e){print('Error is caught here with msg: $e');});
}
}
As to the 'why':
You use a normal try/catch to catch the failures of awaited asynchronous computations. But since you cannot await the constructor, you have to register the callback that handles the exception in another way. I think :)
Since you never awaited the Future that was returned from willThrow(), and you never used the result of the Future, any exception thrown by the function is discarded.
There is no way to write an asynchronous constructor. So you are stuck with using old-school callbacks to handle errors, or simulate an async constructor with a static method:
void main() async {
try {
final t = await Test.create();
await Future.delayed(Duration(seconds: 1));
} catch (e) {
// Never printed
print("caught");
}
}
Future<void> willThrow() async {
throw "error";
}
class Test {
Test._syncCreate() {}
Future<void> _init() async {
await willThrow();
}
static Test create() async {
Test result = Test._syncCreate();
await result._init();
return result;
}
}
I working on error handling of api's. i want if api is crashed then it display a message of "Server is down" something like this, in UI.
I created a class where i'm creating methods of api, here in getBooks method if i modify the api url then it is printing this Exception, and i want it in UI. The problem is getBooks return type is List<Book>> so we can't return this Exception, any solution how to do this?
Exception
E/flutter (12924): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: Exception
here is my api code
class BooksApi {
static Future<List<Book>> getBooks(String query) async {
try {
final url = Uri.parse(
'https://gist.githubusercontent.com/JohannesMilke/d53fbbe9a1b7e7ca2645db13b995dc6f/raw/eace0e20f86cdde3352b2d92f699b6e9dedd8c70/books.json');
final response = await http.get(url);
if (response.statusCode == 200) {
final List books = json.decode(response.body);
return books.map((json) => Book.fromJson(json)).where((book) {
final titleLower = book.title.toLowerCase();
final authorLower = book.author.toLowerCase();
final searchLower = query.toLowerCase();
return titleLower.contains(searchLower) ||
authorLower.contains(searchLower);
}).toList();
} else {
throw Exception;
}
} catch (e) {
print("e");
print(e);
}
throw Exception;
}
}
and calling it like
Future init() async {
setState(() {
isLoading = true;
});
var books = await BooksApi.getBooks(query); //this
var response = await obj.getProduct();
print(response);
setState(() => this.books = books);
setState(() {
isLoading = false;
});
}
You could handle errors with then and onError :
await BooksApi.getBooks(query).then((books) async {
setState(() => {
this.books = books;
this.isLoading = false;
})
}, onError: (error) {
// do something with error
});
or a simple try-catch (you can write try-catch clauses the same way you would in synchronous code).
See handling errors.
You can also use catchError id you don't use async/await :
BooksApi.getBooks(query).then((books) {
setState(() => {
this.books = books;
this.isLoading = false;
})
}).catchError((error, stackTrace) {
print("error is: $error");
});
See futures error handling.
Try to wrap 'var books = await BooksApi.getBooks(query)' with try and catch.
...
try {
var books = await BooksApi.getBooks(query);
} catch (e) {
// To do for UI
}
...
For api, you need to make something like this:
APIModel{
final int code;
// or a success flag
// final bool success;
final String message;
final List<Book> data;
APIModel({this.code,this.message,this.data});
}
It means, every api have its own code,message,and data filed.
When you request, you can check your code or success:
var response = await request(params);
isLoading = false;
if(response.code == 0){}
// or
if(response.success){
// do what you want
}
else {
Toast.show(response.message);
}
You can use build_runner and json_serializable.
I am trying to create an Isolate un Flutter and then use this isolate to fetch some data from Firebase Realtime Database.
I am creating de Isolate in a file called home.dart (not main) and here is my code for that file. I have a class to create the Isolate and the function for the Isolate to execute. Inside this function I am trying to fetch the data.
void elIsolate(SendPort sPort) async {
print("Fetching data");
final databaseReference = FirebaseDatabase.instance.reference().child("categories");
DataSnapshot info;
/*databaseReference.once().then((DataSnapshot snapshot) {
info = snapshot;
print(info.value);
});*/
print("new isolate created");
IsolateChannel channel = IsolateChannel.connectSend(sPort);
channel.stream.listen((data) {
print('newIsolate received : $data');
});
channel.sink.add("hi");
}
class _MyHomePageState extends State<MyHomePage> {
List list = [];
void initState(){
WidgetsFlutterBinding.ensureInitialized();
super.initState();
print("Init state");
loadIsolate();
}
Future loadIsolate() async {
await Firebase.initializeApp();
print("Load isolate");
ReceivePort rPort = ReceivePort();
IsolateChannel channel = IsolateChannel.connectReceive(rPort);
channel.stream.listen((data) {
print('rootIsolate received : $data');
channel.sink.add('How are you');
});
await Isolate.spawn(elIsolate, rPort.sendPort);
/*await Isolate.spawn(getAllWorkers, receivePort.sendPort);
receivePort.listen((message) {
print(message);
});*/
}
}
Then I have my main.dart. I added this line inside the main function: WidgetsFlutterBinding.ensureInitialized();
Here is my code
Future<void> main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
bool resp;
await SharedPreferences.getInstance().then((prefs) {
resp = prefs.getBool('isUser');
if (resp == null) {
FirebaseAuth _auth = FirebaseAuth.instance;
resp = (_auth.currentUser != null);
prefs.setBool('isUser', resp);
}
});
runApp(MyApp(user: resp));
}
flutter_isolate: ^2.0.2
onPressed: () {
FlutterIsolate.spawn(_isolateEntrypoint, "");
}
// A "top level" function (i.e. not inside a class or make it static)
_isolateEntrypoint(String foo) {
WidgetsFlutterBinding.ensureInitialized();
...
}
Make sure that authorization and initialization were made on the same main thread (top level or static).
Now this FlutterEngine will be able to communicate with Firebase Realtime Database but the main FlutterEngine won't. In practice, depending on the app, an app may want to communicate with Realtime Database from either engine (or both). In background apps, more likely from here rather than the main isolate, but again that depends on the app.
In my flutter app, I have a future that handles http requests and returns the decoded data. But I want to be able to send an error if the status code != 200 that can be gotten with the .catchError() handler.
Heres the future:
Future<List> getEvents(String customerID) async {
var response = await http.get(
Uri.encodeFull(...)
);
if (response.statusCode == 200){
return jsonDecode(response.body);
}else{
// I want to return error here
}
}
and when I call this function, I want to be able to get the error like:
getEvents(customerID)
.then(
...
).catchError(
(error) => print(error)
);
Throwing an error/exception:
You can use either return or throw to throw an error or an exception.
Using return:
Future<void> foo() async {
if (someCondition) {
return Future.error('FooError');
}
}
Using throw:
Future<void> bar() async {
if (someCondition) {
throw Exception('BarException');
}
}
Catching the error/exception:
You can use either catchError or try-catch block to catch the error or the exception.
Using catchError:
foo().catchError(print);
Using try-catch:
try {
await bar();
} catch (e) {
print(e);
}
You can use throw :
Future<List> getEvents(String customerID) async {
var response = await http.get(
Uri.encodeFull(...)
);
if (response.statusCode == 200){
return jsonDecode(response.body);
}else{
// I want to return error here
throw("some arbitrary error"); // error thrown
}
}
Another way to solve this is by using the dartz package.
An example of how to use it would look something similar like this
import 'package:dartz/dartz.dart';
abstract class Failure {}
class ServerFailure extends Failure {}
class ResultFailure extends Failure {
final int statusCode;
const ResultFailure({required this.statusCode});
}
FutureOr<Either<Failure, List>> getEvents(String customerID) async {
try {
final response = await http.get(
Uri.encodeFull(...)
);
if (response.statusCode == 200) {
return Right(jsonDecode(response.body));
} else {
return Left(ResultFailure(statusCode: response.statusCode));
}
}
catch (e) {
return Left(ServerFailure());
}
}
main() async {
final result = await getEvents('customerId');
result.fold(
(l) => print('Some failure occurred'),
(r) => print('Success')
);
}
You can return the error data like this if you want to read the error object:
response = await dio.post(endPoint, data: data).catchError((error) {
return error.response;
});
return response;
//POST
Future<String> post_firebase_async({String? path , required Product product}) async {
final Uri _url = path == null ? currentUrl: Uri.https(_baseUrl, '/$path');
print('Sending a POST request at $_url');
final response = await http.post(_url, body: jsonEncode(product.toJson()));
if(response.statusCode == 200){
final result = jsonDecode(response.body) as Map<String,dynamic>;
return result['name'];
}
else{
//throw HttpException(message: 'Failed with ${response.statusCode}');
return Future.error("This is the error", StackTrace.fromString("This is its trace"));
}
}
Here is how to call:
final result = await _firebase.post_firebase_async(product: dummyProduct).
catchError((err){
print('huhu $err');
});