How do I return error from a Future in dart?

Question

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) ); 

Answer 1

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); }