我正在使用RxJava2。
我有一些可观察的，很少有订阅者可以订阅它。
每次新用户到达时，都应该完成一些工作，并且应该通知每个订户。
为此，我决定使用PublishSubject。但是当从第一个订阅者收到doOnSubscribe时，myPublishSubject.hasObservers（）返回false ...
知道为什么会发生这种情况，我该如何解决这个问题？
private val myPublishSubject = PublishSubject.create<Boolean>()
fun getPublishObservable():Observable<Boolean> {
return myPublishSubject.doOnSubscribe {
//do some job when new subscriber arrived and notify all subscribers
//via
myPublishSubject.onNext(true)
}
}
我是否理解这一点，当doOnSubscribe调用它意味着至少有一个订户已经存在？
答案 0 :(得分：0)
我没有找到准备好的答案，所以我创建了自己的主题版本，并将其命名为 RefreshSubject 。
它基于PublishSubject，但有一点不同：如果您想返回observable并在新订阅者到达并准备接收某些数据时收到通知，您应该使用方法getSubscriberReady。
这是一个小例子：
private RefreshSubject<Boolean> refreshSubject = RefreshSubject.create();
//ordinary publish behavior
public Observable<Boolean> getObservable(){
return refreshSubject;
}
//refreshSubject behaviour
public Observable<Boolean> getRefreshObserver(){
return refreshSubject.getSubscriberReady(new Action() {
@Override
public void run() throws Exception {
//new subscriber arrives and ready to receive some data
//so you can make some data request and all your subscribers (with new one just arrived)
//will receive new content
}
});
}
这是全班：
public class RefreshSubject<T> extends Subject<T> {
/** The terminated indicator for the subscribers array. */
@SuppressWarnings("rawtypes")
private static final RefreshSubject.RefreshDisposable[] TERMINATED = new RefreshSubject.RefreshDisposable[0];
/** An empty subscribers array to avoid allocating it all the time. */
@SuppressWarnings("rawtypes")
private static final RefreshSubject.RefreshDisposable[] EMPTY = new RefreshSubject.RefreshDisposable[0];
/** The array of currently subscribed subscribers. */
private final AtomicReference<RefreshDisposable<T>[]> subscribers;
/** The error, write before terminating and read after checking subscribers. */
Throwable error;
/**
* Constructs a RefreshSubject.
* @param <T> the value type
* @return the new RefreshSubject
*/
@CheckReturnValue
public static <T> RefreshSubject<T> create() {
return new RefreshSubject<T>();
}
/**
* Constructs a RefreshSubject.
* @since 2.0
*/
@SuppressWarnings("unchecked")
private RefreshSubject() {
subscribers = new AtomicReference<RefreshSubject.RefreshDisposable<T>[]>(EMPTY);
}
@Override
public void subscribeActual(Observer<? super T> t) {
RefreshSubject.RefreshDisposable<T> ps = new RefreshSubject.RefreshDisposable<T>(t, RefreshSubject.this);
t.onSubscribe(ps);
if (add(ps)) {
// if cancellation happened while a successful add, the remove() didn't work
// so we need to do it again
if (ps.isDisposed()) {
remove(ps);
}
} else {
Throwable ex = error;
if (ex != null) {
t.onError(ex);
} else {
t.onComplete();
}
}
}
public Observable<T> getSubscriberReady(final Action onReady){
return Observable.create(new ObservableOnSubscribe<T>() {
@Override
public void subscribe(ObservableEmitter<T> e) throws Exception {
add(new RefreshDisposable(e, RefreshSubject.this));
onReady.run();
}
});
}
/**
* Tries to add the given subscriber to the subscribers array atomically
* or returns false if the subject has terminated.
* @param ps the subscriber to add
* @return true if successful, false if the subject has terminated
*/
private boolean add(RefreshSubject.RefreshDisposable<T> ps) {
for (;;) {
RefreshSubject.RefreshDisposable<T>[] a = subscribers.get();
if (a == TERMINATED) {
return false;
}
int n = a.length;
@SuppressWarnings("unchecked")
RefreshSubject.RefreshDisposable<T>[] b = new RefreshSubject.RefreshDisposable[n + 1];
System.arraycopy(a, 0, b, 0, n);
b[n] = ps;
if (subscribers.compareAndSet(a, b)) {
return true;
}
}
}
/**
* Atomically removes the given subscriber if it is subscribed to the subject.
* @param ps the subject to remove
*/
@SuppressWarnings("unchecked")
private void remove(RefreshSubject.RefreshDisposable<T> ps) {
for (;;) {
RefreshSubject.RefreshDisposable<T>[] a = subscribers.get();
if (a == TERMINATED || a == EMPTY) {
return;
}
int n = a.length;
int j = -1;
for (int i = 0; i < n; i++) {
if (a[i] == ps) {
j = i;
break;
}
}
if (j < 0) {
return;
}
RefreshSubject.RefreshDisposable<T>[] b;
if (n == 1) {
b = EMPTY;
} else {
b = new RefreshSubject.RefreshDisposable[n - 1];
System.arraycopy(a, 0, b, 0, j);
System.arraycopy(a, j + 1, b, j, n - j - 1);
}
if (subscribers.compareAndSet(a, b)) {
return;
}
}
}
@Override
public void onSubscribe(Disposable s) {
if (subscribers.get() == TERMINATED) {
s.dispose();
}
}
@Override
public void onNext(T t) {
if (subscribers.get() == TERMINATED) {
return;
}
if (t == null) {
onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
return;
}
for (RefreshSubject.RefreshDisposable<T> s : subscribers.get()) {
s.onNext(t);
}
}
@SuppressWarnings("unchecked")
@Override
public void onError(Throwable t) {
if (subscribers.get() == TERMINATED) {
RxJavaPlugins.onError(t);
return;
}
if (t == null) {
t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
}
error = t;
for (RefreshSubject.RefreshDisposable<T> s : subscribers.getAndSet(TERMINATED)) {
s.onError(t);
}
}
@SuppressWarnings("unchecked")
@Override
public void onComplete() {
if (subscribers.get() == TERMINATED) {
return;
}
for (RefreshSubject.RefreshDisposable<T> s : subscribers.getAndSet(TERMINATED)) {
s.onComplete();
}
}
@Override
public boolean hasObservers() {
return subscribers.get().length != 0;
}
@Override
public Throwable getThrowable() {
if (subscribers.get() == TERMINATED) {
return error;
}
return null;
}
@Override
public boolean hasThrowable() {
return subscribers.get() == TERMINATED && error != null;
}
@Override
public boolean hasComplete() {
return subscribers.get() == TERMINATED && error == null;
}
/**
* Wraps the actualEmitter subscriber, tracks its requests and makes cancellation
* to remove itself from the current subscribers array.
*
* @param <T> the value type
*/
private static final class RefreshDisposable<T> extends AtomicBoolean implements Disposable {
private static final long serialVersionUID = 3562861878281475070L;
/** The actualEmitter subscriber. */
final Emitter<? super T> actualEmitter;
/** The actualEmitter subscriber. */
final Observer<? super T> actualObserver;
/** The subject state. */
final RefreshSubject<T> parent;
/**
* Constructs a PublishSubscriber, wraps the actualEmitter subscriber and the state.
* @param actualEmitter the actualEmitter subscriber
* @param parent the parent RefreshProcessor
*/
RefreshDisposable(Emitter<? super T> actualEmitter, RefreshSubject<T> parent) {
this.actualEmitter = actualEmitter;
this.parent = parent;
actualObserver = null;
}
/**
* Constructs a PublishSubscriber, wraps the actualEmitter subscriber and the state.
* @param actualObserver the actualObserver subscriber
* @param parent the parent RefreshProcessor
*/
RefreshDisposable(Observer<? super T> actualObserver, RefreshSubject<T> parent) {
this.actualObserver = actualObserver;
this.parent = parent;
actualEmitter = null;
}
public void onNext(T t) {
if (!get()) {
if (actualEmitter != null)
actualEmitter.onNext(t);
if (actualObserver != null)
actualObserver.onNext(t);
}
}
public void onError(Throwable t) {
if (get()) {
RxJavaPlugins.onError(t);
} else {
if (actualEmitter != null)
actualEmitter.onError(t);
if (actualObserver != null)
actualObserver.onError(t);
}
}
public void onComplete() {
if (!get()) {
if (actualEmitter != null)
actualEmitter.onComplete();
if (actualObserver != null)
actualObserver.onComplete();
}
}
@Override
public void dispose() {
if (compareAndSet(false, true)) {
parent.remove(this);
}
}
@Override
public boolean isDisposed() {
return get();
}
}
}