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 implements Exception {  final _message;  FetchDataException([this._message]);  String toString() { if (_message == null) return "Exception";   return "Exception: $_message";  } }   void loginUser(String email, String password) {   _data     .userLogin(email, password)     .then((user) => _view.onLoginComplete(user))     .catchError((onError) => {        print('error caught');        _view.onLoginError();     }); }  Future < User > userLogin(email, password) async {   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); } 

CatchError doesn't catch the error when the status is not 200. In short error caught is not printed.

Answer 1

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.