How to catch exception in flutter?

Question

This is my exception class. Exception class has been implemented by the abstract exception class of flutter. Am I missing something?

class FetchDataException          


        

Answer 1

To handle errors in an async and await function, use try-catch:

Run the following example to see how to handle an error from an asynchronous function.

Future<void> printOrderMessage() async {
  try {
    var order = await fetchUserOrder();
    print('Awaiting user order...');
    print(order);
  } catch (err) {
    print('Caught error: $err');
  }
}

Future<String> fetchUserOrder() {
  // Imagine that this function is more complex.
  var str = Future.delayed(
      Duration(seconds: 4),
      () => throw 'Cannot locate user order');
  return str;
}

Future<void> main() async {
  await printOrderMessage();
}

Within an async function, you can write try-catch clauses the same way you would in synchronous code.

Answer 2

Try

void loginUser(String email, String password) async {
  try {
    var user = await _data
      .userLogin(email, password);
    _view.onLoginComplete(user);
      });
  } on FetchDataException catch(e) {
    print('error caught: $e');
    _view.onLoginError();
  }
}

catchError is sometimes a bit tricky to get right. With async/await you can use try/catch like with sync code and it is usually much easier to get right.

Answer 3

Future < User > userLogin(email, password) async { try {
  Map body = {
    'username': email,
    'password': password
  };
  http.Response response = await http.post(apiUrl, body: body);
  final responseBody = json.decode(response.body);
  final statusCode = response.statusCode;
  if (statusCode != HTTP_200_OK || responseBody == null) {
    throw new FetchDataException(
      "An error occured : [Status Code : $statusCode]");
   }
  return new User.fromMap(responseBody); }
   catch (e){
    print(e.toString());
}