Finds the single element in this stream matching test.
Like lastWhere, except that it is an error if more than one
matching element occurs in the stream.
Source
Future<T> singleWhere(bool test(T element)) {
_Future<T> future = new _Future<T>();
T result = null;
bool foundResult = false;
StreamSubscription subscription;
subscription = this.listen(
(T value) {
_runUserCode(() => true == test(value), (bool isMatch) {
if (isMatch) {
if (foundResult) {
try {
throw IterableElementError.tooMany();
} catch (e, s) {
_cancelAndErrorWithReplacement(subscription, future, e, s);
}
return;
}
foundResult = true;
result = value;
}
}, _cancelAndErrorClosure(subscription, future));
},
onError: future._completeError,
onDone: () {
if (foundResult) {
future._complete(result);
return;
}
try {
throw IterableElementError.noElement();
} catch (e, s) {
_completeWithErrorCallback(future, e, s);
}
},
cancelOnError: true);
return future;
}