doOnData method
Invokes the given callback function when the stream emits an item. In other implementations, this is called doOnNext.
Example
Stream.fromIterable([1, 2, 3])
  .doOnData(print)
  .listen(null); // prints 1, 2, 3
Implementation
Stream<T> doOnData(void Function(T event) onData) =>
    DoStreamTransformer<T>(onData: onData).bind(this);