Relays are RxJava types which are both an
Observable and a
Subject except without the ability to call
Subjects are useful to bridge the gap between non-Rx APIs. However, they are stateful in a damaging way: when they receive an
onError they no longer become usable for moving data. This is the observable contract and sometimes it is the desired behavior. Most times it is not.
Relays are simply Subjects without the aforementioned property. They allow you to bridge non-Rx APIs into Rx easily, and without the worry of accidentally triggering a terminal state.
As more of your code moves to reactive, the need for Subjects and Relays should diminish. In the transitional period, or for quickly adapting a non-Rx API, Relays provide the convenience of Subjects without the worry of the statefulness of terminal event behavior.
Relay that emits the most recent item it has observed and all subsequent observed items to each subscribed
// observer will receive all events. BehaviorRelay<Object> relay = BehaviorRelay.createDefault("default"); relay.subscribe(observer); relay.accept("one"); relay.accept("two"); relay.accept("three");
// observer will receive the "one", "two" and "three" events, but not "zero" BehaviorRelay<Object> relay = BehaviorRelay.createDefault("default"); relay.accept("zero"); relay.accept("one"); relay.subscribe(observer); relay.accept("two"); relay.accept("three");
Relay that, once an
Observerhas subscribed, emits all subsequently observed items to the subscriber.
PublishRelay<Object> relay = PublishRelay.create(); // observer1 will receive all events relay.subscribe(observer1); relay.accept("one"); relay.accept("two"); // observer2 will only receive "three" relay.subscribe(observer2); relay.accept("three");
Relay that buffers all items it observes and replays them to any
ReplayRelay<Object> relay = ReplayRelay.create(); relay.accept("one"); relay.accept("two"); relay.accept("three"); // both of the following will get the events from above relay.subscribe(observer1); relay.subscribe(observer2);
All relays use the
Relay base class which also allows custom implementations.
See the Javadoc for more information.
(There is no
AsyncRelay since relays have no terminal events to support its behavior.)
<dependency> <groupId>com.jakewharton.rxrelay2</groupId> <artifactId>rxrelay</artifactId> <version>2.1.0</version> </dependency>
Snapshots of the development version are available in Sonatype's
Copyright 2014 Netflix, Inc. Copyright 2015 Jake Wharton Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.