isEmpty property Null safety
Whether this stream contains any elements.
Waits for the first element of this stream, then completes the returned
future with false
.
If this stream ends without emitting any elements, the returned future is
completed with true
.
If the first event is an error, the returned future is completed with that error.
This operation listens to this stream, and a non-broadcast stream cannot be reused after checking whether it is empty.
Implementation
Future<bool> get isEmpty {
_Future<bool> future = new _Future<bool>();
StreamSubscription<T> subscription =
this.listen(null, onError: future._completeError, onDone: () {
future._complete(true);
}, cancelOnError: true);
subscription.onData((_) {
_cancelAndValue(subscription, future, false);
});
return future;
}