catchError method Null safety
Handles errors emitted by this Future.
This is the asynchronous equivalent of a "catch" block.
Returns a new Future that will be completed with either the result of
this future or the result of calling the onError
callback.
If this future completes with a value, the returned future completes with the same value.
If this future completes with an error,
then test
is first called with the error value.
If test
returns false, the exception is not handled by this catchError
,
and the returned future completes with the same error and stack trace
as this future.
If test
returns true
,
onError
is called with the error and possibly stack trace,
and the returned future is completed with the result of this call
in exactly the same way as for then's onError
.
If test
is omitted, it defaults to a function that always returns true.
The test
function should not throw, but if it does, it is handled as
if the onError
function had thrown.
Note that futures don't delay reporting of errors until listeners are
added. If the first catchError
(or then
) call happens after this future
has completed with an error then the error is reported as unhandled error.
See the description on Future.
Example:
Future.delayed(
const Duration(seconds: 1),
() => throw 401,
).then((value) {
throw 'Unreachable';
}).catchError((err) {
print('Error: $err'); // Prints 401.
}, test: (error) {
return error is int && error >= 400;
});
Implementation
@override
Future<T> catchError(Function onError, { bool Function(Object error)? test }) => Completer<T>().future;