doOnListen method
Invokes the given callback function when the stream is first listened to.
Example
Stream.fromIterable([1])
.doOnListen(() => print('Is someone there?'))
.listen(null); // prints 'Is someone there?'
Implementation
Stream<T> doOnListen(void Function() onListen) =>
DoStreamTransformer<T>(onListen: onListen).bind(this);