/**
* 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.
*
* <p>All pre-implemented final methods are thread-safe.
*
* <p>Use the protected {@link #cancel()} to dispose the sequence from within an
* {@code onNext} implementation.
*
* <p>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) <class name> multiple times."}.
*
* <p>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.
*
* <p>Example<pre><code>
* 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!");
* }
* });
* </code></pre>
*
* @param <T> the value type
*/
public abstract class
DefaultObserver<T> implements
Observer<T> {
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() {
}
}