io.reactivex.observers.DefaultObserver Maven / Gradle / Ivy
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/**
* Copyright (c) 2016-present, RxJava Contributors.
*
* 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.
*/
package io.reactivex.observers;
import io.reactivex.Observer;
import io.reactivex.annotations.NonNull;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.util.EndConsumerHelper;
/**
* Abstract base implementation of an {@link io.reactivex.Observer Observer} with support for cancelling a
* subscription via {@link #cancel()} (synchronously) and calls {@link #onStart()}
* when the subscription happens.
*
* All pre-implemented final methods are thread-safe.
*
*
Use the protected {@link #cancel()} to dispose the sequence from within an
* {@code onNext} implementation.
*
*
Like all other consumers, {@code DefaultObserver} can be subscribed only once.
* Any subsequent attempt to subscribe it to a new source will yield an
* {@link IllegalStateException} with message {@code "It is not allowed to subscribe with a(n) multiple times."}.
*
* Implementation of {@link #onStart()}, {@link #onNext(Object)}, {@link #onError(Throwable)}
* and {@link #onComplete()} are not allowed to throw any unchecked exceptions.
* If for some reason this can't be avoided, use {@link io.reactivex.Observable#safeSubscribe(io.reactivex.Observer)}
* instead of the standard {@code subscribe()} method.
*
*
Example
* Observable.range(1, 5)
* .subscribe(new DefaultObserver<Integer>() {
* @Override public void onStart() {
* System.out.println("Start!");
* }
* @Override public void onNext(Integer t) {
* if (t == 3) {
* cancel();
* }
* System.out.println(t);
* }
* @Override public void onError(Throwable t) {
* t.printStackTrace();
* }
* @Override public void onComplete() {
* System.out.println("Done!");
* }
* });
*
*
* @param the value type
*/
public abstract class DefaultObserver implements Observer {
private Disposable upstream;
@Override
public final void onSubscribe(@NonNull Disposable d) {
if (EndConsumerHelper.validate(this.upstream, d, getClass())) {
this.upstream = d;
onStart();
}
}
/**
* Cancels the upstream's disposable.
*/
protected final void cancel() {
Disposable upstream = this.upstream;
this.upstream = DisposableHelper.DISPOSED;
upstream.dispose();
}
/**
* Called once the subscription has been set on this observer; override this
* to perform initialization.
*/
protected void onStart() {
}
}