LifecycleTransformer.java 文件源码

/**
 * NOTE: This throws a NoSuchElementException if the item is filtered out since a Single can't be empty, so the 
 * onError is called after onDestroy() when using Single().
 *
 * @param upstream
 * @return
 */
@Override
public SingleSource<T> apply(Single<T> upstream) {
    Single<T> transformedStream = upstream
            .cache() // Cache to replay emitted values to late subscriber
            .filter(filterIfDestroyedPredicate) // Filter to stop emitting items once LifecycleOwner is destroyed
            .toSingle();
    setReactiveType((R)transformedStream);

    return transformedStream;
}