combineLatest
combineLatest操作符的作用是组合发射的数据，通过 Func 类来组装多个 Observable 发射的数据, 等到最后一个 Observable 发射数据了, 然后把所有发射的数据交给Fun进行组合, 然后把组合后的数据发射出去。
Observable observable1 = Observable.just(1);
Observable observable2 = Observable.just(2);
Observable observable3 = Observable.just(3);
Observable.combineLatest(observable1, observable2, observable3, new Function3<Integer, Integer, Integer, String>() {
@NotNull
@Override
public String apply(@NotNull Integer integer, @NotNull Integer integer2, @NotNull Integer integer3) throws Exception {
return (integer + integer2 +integer3)+ "";
}
}).subscribe(new Observer<String>() {
@Override
public void onSubscribe(@NotNull Disposable d) {
System.out.println("onSubscribe");
}
@Override
public void onNext(@NotNull String s) {
System.out.println("onNext "+ s);
}
@Override
public void onError(@NotNull Throwable e) {
System.out.println(e.getMessage());
}
@Override
public void onComplete() {
System.out.println("onComplete");
}
});
输出
onSubscribe
onNext 6
onComplete
看看源码
public static <T1, T2, T3, R> Observable<R> combineLatest(
...
return combineLatest(Functions.toFunction(combiner), bufferSize(), source1, source2, source3);
}
Functions.toFunction(combiner)的作用是把combiner对象转换成Function对象，将T1, T2, T3转换成结果R
public static <T1, T2, T3, R> Function<Object[], R> toFunction(final Function3<T1, T2, T3, R> f) {
...
return new Array3Func<T1, T2, T3, R>(f);
}
static final class Array3Func<T1, T2, T3, R> implements Function<Object[], R> {
final Function3<T1, T2, T3, R> f;
Array3Func(Function3<T1, T2, T3, R> f) {
this.f = f;
}
@SuppressWarnings("unchecked")
@Override
public R apply(Object[] a) throws Exception {
if (a.length != 3) {
throw new IllegalArgumentException("Array of size 3 expected but got " + a.length);
}
return f.apply((T1)a[0], (T2)a[1], (T3)a[2]);
}
}
public static <T, R> Observable<R> combineLatest(Function<? super Object[], ? extends R> combiner, int bufferSize, ObservableSource<? extends T>... sources) {
return combineLatest(sources, combiner, bufferSize);
}
public static <T, R> Observable<R> combineLatest(ObservableSource<? extends T>[] sources,
Function<? super Object[], ? extends R> combiner, int bufferSize) {
...
int s = bufferSize << 1;
return RxJavaPlugins.onAssembly(new ObservableCombineLatest<T, R>(sources, null, combiner, s, false));
}
转换成ObservableCombineLatest对象，delayError 顾名思义，当出现错误时，是否会延迟onError的执行。
为什么会出现这样的情况，因为消费的方法均是在Scheduler中执行的，因此会有生产和消费速率不一致的情形。那么当出现错误时，可能队列里还有数据未传递给下游，因此delayError这个参数就是为了解决这个问题
。delayEror默认为false, 当出现错误时会直接越过未消费的队列中的数据，在下游处理完当前的数据后会立即执行onError。
如果为true则会保持和上游一致的顺序向下游调度onNext，最后执行onError。后面会分析。
bufferSize是队列SpscLinkedArrayQueue的长度，长度最小是8。
public final class ObservableCombineLatest<T, R> extends Observable<R> {
final ObservableSource<? extends T>[] sources;
final Iterable<? extends ObservableSource<? extends T>> sourcesIterable;
final Function<? super Object[], ? extends R> combiner;
final int bufferSize;
final boolean delayError;
public ObservableCombineLatest(ObservableSource<? extends T>[] sources,
Iterable<? extends ObservableSource<? extends T>> sourcesIterable,
Function<? super Object[], ? extends R> combiner, int bufferSize,
boolean delayError) {
this.sources = sources;
this.sourcesIterable = sourcesIterable;
this.combiner = combiner;
this.bufferSize = bufferSize;
this.delayError = delayError;
}
@Override
@SuppressWarnings("unchecked")
public void subscribeActual(Observer<? super R> observer) {
ObservableSource<? extends T>[] sources = this.sources;
int count = 0;
...
LatestCoordinator<T, R> lc = new LatestCoordinator<T, R>(observer, combiner, count, bufferSize, delayError);
lc.subscribe(sources);
}
LatestCoordinator构造函数里创建了CombinerObserver数组。
LatestCoordinator(Observer<? super R> actual,
Function<? super Object[], ? extends R> combiner,
int count, int bufferSize, boolean delayError) {
this.downstream = actual;
this.combiner = combiner;
this.delayError = delayError;
this.latest = new Object[count];
CombinerObserver<T, R>[] as = new CombinerObserver[count];
for (int i = 0; i < count; i++) {
as[i] = new CombinerObserver<T, R>(this, i);
}
this.observers = as;
this.queue = new SpscLinkedArrayQueue<Object[]>(bufferSize);
}
sources[i].subscribe(as[i]);用来订阅CombinerObserver,数据经过这个对象,然后交给
LatestCoordinator处理。
数据本来可以直接发送给观察者。
经过LatestCoordinator的数据处理，将数据组合后重新发送给观察者。
public void subscribe(ObservableSource<? extends T>[] sources) {
Observer<T>[] as = observers;
int len = as.length;
downstream.onSubscribe(this);
for (int i = 0; i < len; i++) {
if (done || cancelled) {
return;
}
sources[i].subscribe(as[i]);
}
}
static final class CombinerObserver<T, R> extends AtomicReference<Disposable> implements Observer<T> {
private static final long serialVersionUID = -4823716997131257941L;
final LatestCoordinator<T, R> parent;
final int index;
CombinerObserver(LatestCoordinator<T, R> parent, int index) {
this.parent = parent;
this.index = index;
}
@Override
public void onSubscribe(Disposable d) {
DisposableHelper.setOnce(this, d);
}
@Override
public void onNext(T t) {
parent.innerNext(index, t);
}
@Override
public void onError(Throwable t) {
parent.innerError(index, t);
}
@Override
public void onComplete() {
parent.innerComplete(index);
}
public void dispose() {
DisposableHelper.dispose(this);
}
}
LatestCoordinator内部的innerNext的方法中，latest表示最新的数据，当发送的数据量和被观察者一样时，就可以把数据放到队列中，drain的含义时排空，就是把数据打包发送给下游
void innerNext(int index, T item) {
boolean shouldDrain = false;
synchronized (this) {
Object[] latest = this.latest;
if (latest == null) {
return;
}
Object o = latest[index];
int a = active;
if (o == null) {
active = ++a;
}
latest[index] = item;
if (a == latest.length) {
queue.offer(latest.clone());
shouldDrain = true;
}
}
if (shouldDrain) {
drain();
}
}
done表示所有生产者都已经把数据发送完成或者还没有发送就出错。因为getAndIncrement的意思是原子加1，并且返回原来的值，第一次进入drain函数，getAndIncrement()返回的结果就是0，现在原子变量已经变成了1，阻止其他线程再次调用。addAndGet表示原子加上一个值，并且返回更新后的值， 第一层的for循环持续更新原子变量，一直把值更新到原来的0，第二层的for循环是要把数据给排空，排出数据的过程中，很可能出现生产者出错，有2种策略，要么把数据排空后调用error，要么不要queue里的数据了，直接调用error，这就要用delayError控制了，为true时就是第一种，为false时就是第二种。
void drain() {
//多线程安全控制
if (getAndIncrement() != 0) {
return;
}
final SpscLinkedArrayQueue<Object[]> q = queue;
final Observer<? super R> a = downstream;
final boolean delayError = this.delayError;
int missed = 1;
for (;;) {
for (;;) {
if (cancelled) {
clear(q);
return;
}
//delayError 默认是fasle，表示一旦出错，队列里还有没有发送给观察者的数据就要被遗弃掉了
if (!delayError && errors.get() != null) {
cancelSources();
clear(q);
a.onError(errors.terminate());
return;
}
boolean d = done;
Object[] s = q.poll(); //弹出数据
boolean empty = s == null;
//保证数据被排空
//没有出错，就是onComplete
if (d && empty) {
clear(q);
Throwable ex = errors.terminate();
if (ex == null) {
a.onComplete();
} else {
a.onError(ex);
}
return;
}
if (empty) {
break;
}
R v;
try {
//转换数据
v = ObjectHelper.requireNonNull(combiner.apply(s), "The combiner returned a null value");
} catch (Throwable ex) {
Exceptions.throwIfFatal(ex);
errors.addThrowable(ex);
cancelSources();
clear(q);
ex = errors.terminate();
a.onError(ex);
return;
}
//重新发送给观察者
a.onNext(v);
}
missed = addAndGet(-missed);
if (missed == 0) {
//原子更新成功
break;
}
}
}
latest[index] == null;表示生产者还没有发送数据。
void innerError(int index, Throwable ex) {
if (errors.addThrowable(ex)) {
boolean cancelOthers = true;
if (delayError) {
//delayError为true时，
synchronized (this) {
Object[] latest = this.latest;
if (latest == null) {
return;
}
//还没有发送数据，就已经出错，后面的数据也就没有必要发送了。
cancelOthers = latest[index] == null;
if (cancelOthers || ++complete == latest.length) {
done = true;
}
}
}
if (cancelOthers) {
cancelSources();
}
drain();
} else {
RxJavaPlugins.onError(ex);
}
}
Android中经常用它提交表单,当用户名和密码都被填写后，登录按钮才能使用。
disposables += Observable.combineLatest(
view.onNameChanged(), view.onEmailChanged(), ::AccountInfo)
.subscribe { accountInfo ->
view.setNextStepButtonEnabled(accountInfo.isValid())
}
combineLatestDelayError
combineLatestDelayError就是会设置delayError为true。
Observable o1 = Observable.create(new ObservableOnSubscribe<Integer>() {
@Override
public void subscribe(@NotNull ObservableEmitter<Integer> emitter) throws Exception {
emitter.onNext(1);
emitter.onNext(2);
emitter.onNext(3);
}
});
Observable o2 = Observable.create(new ObservableOnSubscribe<Integer>() {
@Override
public void subscribe(@NotNull ObservableEmitter<Integer> emitter) throws Exception {
//emitter.onError(new Exception("我死了~")); 会调用onError
emitter.onNext(4);
emitter.onNext(5);
emitter.onError(new Exception("我死了~")); //不会调用onError，事件流停止
emitter.onNext(6);
}
});
Observable.combineLatestDelayError(new Function<Object[], String>() {
@Override
public String apply(@NotNull Object[] objects) throws Exception {
StringBuilder sb = new StringBuilder();
Arrays.stream(objects).forEach(o -> sb.append(o).append("-"));
return sb.toString();
}
}, 2, o1, o2).subscribe(new Observer() {
@Override
public void onSubscribe(@NotNull Disposable d) {
System.out.println("onSubscribe");
}
@Override
public void onNext(@NotNull Object o) {
System.out.println("onNext " + o);
}
@Override
public void onError(@NotNull Throwable e) {
System.out.println("onError " + e.getMessage());
}
@Override
public void onComplete() {
System.out.println("onComplete");
}
});
