rx.internal.operators.OperatorTake Maven / Gradle / Ivy
Show all versions of rxjava-core Show documentation
/**
* Copyright 2014 Netflix, Inc.
*
* 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 rx.internal.operators;
import rx.Observable.Operator;
import rx.Producer;
import rx.Subscriber;
/**
* An {@code Observable} that emits the first {@code num} items emitted by the source {@code Observable}.
*
* 
*
* You can choose to pay attention only to the first {@code num} items emitted by an {@code Observable} by using
* the {@code take} operator. This operator returns an {@code Observable} that will invoke a subscriber's
* {@link Subscriber#onNext onNext} function a maximum of {@code num} times before invoking
* {@link Subscriber#onCompleted onCompleted}.
*/
public final class OperatorTake implements Operator {
final int limit;
public OperatorTake(int limit) {
this.limit = limit;
}
@Override
public Subscriber call(final Subscriber child) {
final Subscriber parent = new Subscriber() {
int count = 0;
boolean completed = false;
@Override
public void onCompleted() {
if (!completed) {
child.onCompleted();
}
}
@Override
public void onError(Throwable e) {
if (!completed) {
child.onError(e);
}
}
@Override
public void onNext(T i) {
if (!isUnsubscribed()) {
child.onNext(i);
if (++count >= limit) {
completed = true;
child.onCompleted();
unsubscribe();
}
}
}
/**
* We want to adjust the requested values based on the `take` count.
*/
@Override
public void setProducer(final Producer producer) {
child.setProducer(new Producer() {
@Override
public void request(long n) {
long c = limit - count;
if (n < c) {
producer.request(n);
} else {
producer.request(c);
}
}
});
}
};
if (limit == 0) {
child.onCompleted();
parent.unsubscribe();
}
/*
* We decouple the parent and child subscription so there can be multiple take() in a chain such as for
* the groupBy Observer use case where you may take(1) on groups and take(20) on the children.
*
* Thus, we only unsubscribe UPWARDS to the parent and an onComplete DOWNSTREAM.
*
* However, if we receive an unsubscribe from the child we still want to propagate it upwards so we
* register 'parent' with 'child'
*/
child.add(parent);
return parent;
}
}