DoStreamTransformer<S> class

Invokes the given callback at the corresponding point the the stream lifecycle. For example, if you pass in an onDone callback, it will be invoked when the stream finishes emitting items.

This transformer can be used for debugging, logging, etc. by intercepting the stream at different points to run arbitrary actions.

It is possible to hook onto the following parts of the stream lifecycle:

  • onCancel
  • onData
  • onDone
  • onError
  • onListen
  • onPause
  • onResume

In addition, the onEach argument is called at onData, onDone, and onError with a Notification passed in. The Notification argument contains the Kind of event (OnData, OnDone, OnError), and the item or error that was emitted. In the case of onDone, no data is emitted as part of the Notification.

If no callbacks are passed in, a runtime error will be thrown in dev mode in order to 'fail fast' and alert the developer that the transformer should be used or safely removed.

Example

Stream.fromIterable([1])
    .transform(DoStreamTransformer(
      onData: print,
      onError: (e, s) => print('Oh no!'),
      onDone: () => print('Done')))
    .listen(null); // Prints: 1, 'Done'
Inheritance

Constructors

DoStreamTransformer({FutureOr<void> onCancel()?, void onData(S event)?, void onDone()?, void onEach(Notification<S> notification)?, void onError(Object, StackTrace)?, void onListen()?, void onPause()?, void onResume()?})
Constructs a StreamTransformer which will trigger any of the provided handlers as they occur.

Properties

hashCode → int
The hash code for this object.
no setterinherited
onCancel → FutureOr<void> Function()?
fires when all subscriptions have cancelled.
final
onData → void Function(S event)?
fires when data is emitted
final
onDone → void Function()?
fires on close
final
onEach → void Function(Notification<S> notification)?
fires on data, close and error
final
onError → void Function(Object, StackTrace)?
fires on errors
final
onListen → void Function()?
fires when a subscription first starts
final
onPause → void Function()?
fires when the subscription pauses
final
onResume → void Function()?
fires when the subscription resumes
final
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

bind(Stream<S> stream) → Stream<S>
Transforms the provided stream.
override
cast<RS, RT>() → StreamTransformer<RS, RT>
Provides a StreamTransformer<RS, RT> view of this stream transformer.
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited