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Android开源库——RxJava和RxAndroid

2025/3/16 17:37:20 来源：https://blog.csdn.net/qq_35258036/article/details/146109458  浏览:  次   关键词：Android开源库——RxJava和RxAndroid

RxJava和RxAndroid是什么？

RxJava是基于JVM的响应式扩展，用于编写异步代码

RxAndroid是关于Android的RxJava绑定

RxJava和RxAndroid使用

依赖

implementation 'io.reactivex.rxjava3:rxjava:3.1.0'
implementation 'io.reactivex.rxjava3:rxandroid:3.0.2'

使用过程

如下模拟在子线程中进行耗时操作，并将结果返回到主线程中处理

  • Flowable：将要进行的操作
  • subscribeOn()：操作要运行的线程
  • observeOn() ：处理结果要运行的线程
  • subscribe()：处理结果
Flowable.fromCallable(() -> {Thread.sleep(1000);return "Done";}).subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()).subscribe(System.out::println, Throwable::printStackTrace);
Flowable<String> source = Flowable.fromCallable(() -> {Thread.sleep(1000); return "Done";
});
Flowable<String> runBackground = source.subscribeOn(Schedulers.io());
Flowable<String> showForeground = runBackground.observeOn(AndroidSchedulers.mainThread());
showForeground.subscribe(System.out::println, Throwable::printStackTrace);

RxJava源码解析

Publisher

Publisher用于发布数据，Subscriber通过subscribe()订阅数据

public interface Publisher<T> {public void subscribe(Subscriber<? super T> s);
}

Subscriber

Subscriber接收Publisher发布的数据

  • onSubscribe()：subscribe()回调函数，回调前会创建Subscription用于控制数据发布和停止
  • onNext()：当Subscription调用request()时会调用onNext()发布数据
  • onError()：处理接收到的错误
  • onComplete()：处理完成的情况
public interface Subscriber<T> {public void onSubscribe(Subscription s);public void onNext(T t);public void onError(Throwable t);public void onComplete();
}

Subscription

Subscription表示Publisher和Subscriber的对应关系

  • request()：向Publisher请求数据
  • cancel()：让Publisher停止发布数据
public interface Subscription {public void request(long n);public void cancel();
}

Scheduler

createWorker()用于创建Worker ，具体的调度工作由Worker的schedule()完成

public abstract class Scheduler {public abstract Worker createWorker();public abstract static class Worker implements Disposable {@NonNullpublic Disposable schedule(@NonNull Runnable run) {return schedule(run, 0L, TimeUnit.NANOSECONDS);}public abstract Disposable schedule(@NonNull Runnable run, long delay, @NonNull TimeUnit unit);}
}

source传递过程

fromCallable()创建FlowableFromCallable，传递callable

public abstract class Flowable<@NonNull T> implements Publisher<T> {public static <@NonNull T> Flowable<T> fromCallable(@NonNull Callable<? extends T> callable) {return RxJavaPlugins.onAssembly(new FlowableFromCallable<>(callable));}
}

subscribeOn()创建FlowableSubscribeOn，传递this（即FlowableFromCallable）作为source

public abstract class Flowable<@NonNull T> implements Publisher<T> {public final Flowable<T> subscribeOn(@NonNull Scheduler scheduler) {Objects.requireNonNull(scheduler, "scheduler is null");return subscribeOn(scheduler, !(this instanceof FlowableCreate));}public final Flowable<T> subscribeOn(@NonNull Scheduler scheduler, boolean requestOn) {Objects.requireNonNull(scheduler, "scheduler is null");return RxJavaPlugins.onAssembly(new FlowableSubscribeOn<>(this, scheduler, requestOn));}
}

observeOn()创建FlowableObserveOn，传递this（即FlowableSubscribeOn）作为source

public abstract class Flowable<@NonNull T> implements Publisher<T> {public final Flowable<T> observeOn(@NonNull Scheduler scheduler) {return observeOn(scheduler, false, bufferSize());}public final Flowable<T> observeOn(@NonNull Scheduler scheduler, boolean delayError, int bufferSize) {Objects.requireNonNull(scheduler, "scheduler is null");ObjectHelper.verifyPositive(bufferSize, "bufferSize");return RxJavaPlugins.onAssembly(new FlowableObserveOn<>(this, scheduler, delayError, bufferSize));}
}

即依次将自身当作Flowable，作为参数source传递给下一个Flowable

subscribe()流程

subscribe()最终调用具体Flowable的subscribeActual()

public abstract class Flowable<@NonNull T> implements Publisher<T> {......public final Disposable subscribe(@NonNull Consumer<? super T> onNext, @NonNull Consumer<? super Throwable> onError) {return subscribe(onNext, onError, Functions.EMPTY_ACTION);}public final Disposable subscribe(@NonNull Consumer<? super T> onNext, @NonNull Consumer<? super Throwable> onError,@NonNull Action onComplete) {.....LambdaSubscriber<T> ls = new LambdaSubscriber<>(onNext, onError, onComplete, FlowableInternalHelper.RequestMax.INSTANCE);subscribe(ls);return ls;}public final void subscribe(@NonNull FlowableSubscriber<? super T> subscriber) {try {Subscriber<? super T> flowableSubscriber = RxJavaPlugins.onSubscribe(this, subscriber);......subscribeActual(flowableSubscriber);}......}protected abstract void subscribeActual(@NonNull Subscriber<? super T> subscriber);
}

调用过程和传递过程是相反的，先调用FlowableObserveOn的subscribeActual()

public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {......@Overridepublic void subscribeActual(Subscriber<? super T> s) {Worker worker = scheduler.createWorker();if (s instanceof ConditionalSubscriber) {.....} else {source.subscribe(new ObserveOnSubscriber<>(s, worker, delayError, prefetch));}}}

上面的source就是上一层传递下来的FlowableSubscribeOn，即调用到FlowableSubscribeOn的subscribeActual()

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {......@Overridepublic void subscribeActual(final Subscriber<? super T> s) {Scheduler.Worker w = scheduler.createWorker();final SubscribeOnSubscriber<T> sos = new SubscribeOnSubscriber<>(s, w, source, nonScheduledRequests);.....w.schedule(sos);}static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>implements FlowableSubscriber<T>, Subscription, Runnable {......@Overridepublic void run() {lazySet(Thread.currentThread());Publisher<T> src = source;source = null;src.subscribe(this);}

schedule()最终会调用run()方法，lazySet()切换线程，上面的source就是上一层传递下来的FlowableFromCallable，即将到FlowableFromCallable的subscribeActual()放到指定线程中运行

public final class FlowableFromCallable<T> extends Flowable<T> implements Supplier<T> {final Callable<? extends T> callable;......@Overridepublic void subscribeActual(Subscriber<? super T> s) {DeferredScalarSubscription<T> deferred = new DeferredScalarSubscription<>(s);s.onSubscribe(deferred);T t;try {t = Objects.requireNonNull(callable.call(), "The callable returned a null value");} catch (Throwable ex) {Exceptions.throwIfFatal(ex);if (deferred.isCancelled()) {RxJavaPlugins.onError(ex);} else {s.onError(ex);}return;}deferred.complete(t);}......
}

上面若出错回调onError()，否则调用downstream的onNext()传递结果

public class DeferredScalarSubscription<@NonNull T> extends BasicIntQueueSubscription<T> {public final void complete(T v) {int state = get();for (;;) {......if (state == HAS_REQUEST_NO_VALUE) {lazySet(HAS_REQUEST_HAS_VALUE);Subscriber<? super T> a = downstream;a.onNext(v);if (get() != CANCELLED) {a.onComplete();}return;}value = v;......}}
}

onNext()过程

调用FlowableSubscribeOn.SubscribeOnSubscriber的onNext()，调用downstream的onNext()传递结果

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>implements FlowableSubscriber<T>, Subscription, Runnable {@Overridepublic void onNext(T t) {downstream.onNext(t);}}
}

调用FlowableObserveOn.BaseObserveOnSubscriber的onNext()、trySchedule()，schedule()最终会调用run()方法，根据sourceMode判断是同步还是异步

  • FlowableObserveOn.ObserveOnSubscriber的runSync()和runAsync()都调用downstream的onNext()传递结果
public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {.....abstract static class BaseObserveOnSubscriber<T>extends BasicIntQueueSubscription<T>implements FlowableSubscriber<T>, Runnable {@Overridepublic final void onNext(T t) {......trySchedule();}'final void trySchedule() {......worker.schedule(this);}@Overridepublic final void run() {if (outputFused) {runBackfused();} else if (sourceMode == SYNC) {runSync();} else {runAsync();}}}static final class ObserveOnSubscriber<T> extends BaseObserveOnSubscriber<T>implements FlowableSubscriber<T> {void runSync() {......final Subscriber<? super T> a = downstream;......for (;;) {......while (e != r) {......a.onNext(v);......}......}}.....@Overridevoid runAsync() {final Subscriber<? super T> a = downstream;for (;;) {......while (e != r) {.....a.onNext(v);.....}.....}}}
}

调用LambdaSubscriber的onNext()，通过传入的Consumer消费掉最终的结果，即通过System.out::println打印出来

public final class LambdaSubscriber<T> extends AtomicReference<Subscription>implements FlowableSubscriber<T>, Subscription, Disposable, LambdaConsumerIntrospection {.....@Overridepublic void onNext(T t) {if (!isDisposed()) {try {onNext.accept(t);} catch (Throwable e) {Exceptions.throwIfFatal(e);get().cancel();onError(e);}}}
}

onSubscribe()和request()流程

FlowableFromCallable回调下一层的onSubscribe()，其将Subscription存到upstream

public final class FlowableFromCallable<T> extends Flowable<T> implements Supplier<T> {final Callable<? extends T> callable;@Overridepublic void subscribeActual(Subscriber<? super T> s) {DeferredScalarSubscription<T> deferred = new DeferredScalarSubscription<>(s);s.onSubscribe(deferred);......}
}public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>implements FlowableSubscriber<T>, Subscription, Runnable {@Overridepublic void onSubscribe(Subscription s) {if (SubscriptionHelper.setOnce(this.upstream, s)) {......}}}
}

FlowableSubscribeOn回调下一层的onSubscribe()，其回调下一层的onSubscribe()和上一层的request()请求数据

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {......@Overridepublic void subscribeActual(final Subscriber<? super T> s) {Scheduler.Worker w = scheduler.createWorker();final SubscribeOnSubscriber<T> sos = new SubscribeOnSubscriber<>(s, w, source, nonScheduledRequests);s.onSubscribe(sos);}   
}public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {static final class ObserveOnSubscriber<T> extends BaseObserveOnSubscriber<T>implements FlowableSubscriber<T> {......@Overridepublic void onSubscribe(Subscription s) {if (SubscriptionHelper.validate(this.upstream, s)) {this.upstream = s;......queue = new SpscArrayQueue<>(prefetch);downstream.onSubscribe(this);s.request(prefetch);}}}
}

LambdaSubscriber利用FlowableInternalHelper.RequestMax的accept()调用上一层的request()，从schedule()获取数据

public final class LambdaSubscriber<T> extends AtomicReference<Subscription>implements FlowableSubscriber<T>, Subscription, Disposable, LambdaConsumerIntrospection {@Overridepublic void onSubscribe(Subscription s) {if (SubscriptionHelper.setOnce(this, s)) {try {onSubscribe.accept(this);} catch (Throwable ex) {......}}}}public final class FlowableInternalHelper {public enum RequestMax implements Consumer<Subscription> {INSTANCE;@Overridepublic void accept(Subscription t) {t.request(Long.MAX_VALUE);}}
}public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {abstract static class BaseObserveOnSubscriber<T>extends BasicIntQueueSubscription<T>implements FlowableSubscriber<T>, Runnable {@Overridepublic final void request(long n) {if (SubscriptionHelper.validate(n)) {BackpressureHelper.add(requested, n);trySchedule();}}final void trySchedule() {......worker.schedule(this);}}
}

FlowableSubscribeOn.SubscribeOnSubscriber的request()、requestUpstream()判断当前线程，若未切换线程调用schedule()切换线程调用上一层的request()

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>implements FlowableSubscriber<T>, Subscription, Runnable {@Overridepublic void request(final long n) {if (SubscriptionHelper.validate(n)) {Subscription s = this.upstream.get();if (s != null) {requestUpstream(n, s);} else {......}}}}void requestUpstream(final long n, final Subscription s) {if (nonScheduledRequests || Thread.currentThread() == get()) {s.request(n);} else {worker.schedule(new Request(s, n));}}static final class Request implements Runnable {......@Overridepublic void run() {upstream.request(n);}}}
}

DeferredScalarSubscription接收到请求后，将值传给downstream的onNext()

public class DeferredScalarSubscription<@NonNull T> extends BasicIntQueueSubscription<T> {@Overridepublic final void request(long n) {if (SubscriptionHelper.validate(n)) {for (;;) {int state = get();......if (state == NO_REQUEST_HAS_VALUE) {if (compareAndSet(NO_REQUEST_HAS_VALUE, HAS_REQUEST_HAS_VALUE)) {T v = value;if (v != null) {value = null;Subscriber<? super T> a = downstream;a.onNext(v);if (get() != CANCELLED) {a.onComplete();}}}return;}......}}}
}

Schedulers.io()调度过程

Schedulers.io() = Schedulers.IO = IOTask() = IoHolder.DEFAULT = IoScheduler()

public final class Schedulers {static final Scheduler IO;static final class IoHolder {static final Scheduler DEFAULT = new IoScheduler();}static {IO = RxJavaPlugins.initIoScheduler(new IOTask());}public static Scheduler io() {return RxJavaPlugins.onIoScheduler(IO);}static final class IOTask implements Supplier<Scheduler> {@Overridepublic Scheduler get() {return IoHolder.DEFAULT;}}
}

FlowableSubscribeOn的subscribeActual()通过IoScheduler创建Worker并调用schedule()

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {......@Overridepublic void subscribeActual(final Subscriber<? super T> s) {Scheduler.Worker w = scheduler.createWorker();final SubscribeOnSubscriber<T> sos = new SubscribeOnSubscriber<>(s, w, source, nonScheduledRequests);.....w.schedule(sos);}
}

调用IoScheduler的createWorker()会返回EventLoopWorker

public final class IoScheduler extends Scheduler {@NonNull@Overridepublic Worker createWorker() {return new EventLoopWorker(pool.get());}
}

调用IoScheduler.EventLoopWorker的schedule()最终调用ThreadWorker的父类NewThreadWorker的scheduleActual()

public final class IoScheduler extends Scheduler {static final class EventLoopWorker extends Scheduler.Worker implements Runnable {@NonNull@Overridepublic Disposable schedule(@NonNull Runnable action, long delayTime, @NonNull TimeUnit unit) {......return threadWorker.scheduleActual(action, delayTime, unit, tasks);}}static final class ThreadWorker extends NewThreadWorker {......}
}

调用scheduleActual()将Runnable封装成ScheduledRunnable，通过ScheduledThreadPoolExecutor的submit()或schedule()提交

public class NewThreadWorker extends Scheduler.Worker implements Disposable {private final ScheduledExecutorService executor;volatile boolean disposed;public NewThreadWorker(ThreadFactory threadFactory) {executor = SchedulerPoolFactory.create(threadFactory);}@NonNullpublic ScheduledRunnable scheduleActual(final Runnable run, long delayTime, @NonNull TimeUnit unit, @Nullable DisposableContainer parent) {Runnable decoratedRun = RxJavaPlugins.onSchedule(run);ScheduledRunnable sr = new ScheduledRunnable(decoratedRun, parent);......Future<?> f;try {if (delayTime <= 0) {f = executor.submit((Callable<Object>)sr);} else {f = executor.schedule((Callable<Object>)sr, delayTime, unit);}sr.setFuture(f);} catch (RejectedExecutionException ex) {......}return sr;}
}public final class SchedulerPoolFactory {public static ScheduledExecutorService create(ThreadFactory factory) {final ScheduledThreadPoolExecutor exec = new ScheduledThreadPoolExecutor(1, factory);exec.setRemoveOnCancelPolicy(PURGE_ENABLED);return exec;}
}

线程池会调用FlowableSubscribeOn.SubscribeOnSubscriber的run()方法，SubscribeOnSubscriber继承了AtomicReference<Thread>，lazySet()切换线程调用上一层source的subscribe()

public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>implements FlowableSubscriber<T>, Subscription, Runnable {@Overridepublic void run() {lazySet(Thread.currentThread());Publisher<T> src = source;source = null;src.subscribe(this);}}}

AndroidSchedulers.mainThread()调度过程

AndroidSchedulers.mainThread() = AndroidSchedulers.MAIN_THREAD = MainHolder.DEFAULT = HandlerScheduler()，通过主线程Looper创建handler

public final class AndroidSchedulers {private static final class MainHolder {static final Scheduler DEFAULT = internalFrom(Looper.getMainLooper(), true);}private static final Scheduler MAIN_THREAD =RxAndroidPlugins.initMainThreadScheduler(() -> MainHolder.DEFAULT);}public static Scheduler mainThread() {return RxAndroidPlugins.onMainThreadScheduler(MAIN_THREAD);}private static Scheduler internalFrom(Looper looper, boolean async) {......return new HandlerScheduler(new Handler(looper), async);}
}

FlowableObserveOn的subscribeActual()通过IoScheduler创建Worker，在onNext()的trySchedule()调用schedule()

public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {@Overridepublic void subscribeActual(Subscriber<? super T> s) {Worker worker = scheduler.createWorker();if (s instanceof ConditionalSubscriber) {......} else {source.subscribe(new ObserveOnSubscriber<>(s, worker, delayError, prefetch));}}abstract static class BaseObserveOnSubscriber<T>extends BasicIntQueueSubscription<T>implements FlowableSubscriber<T>, Runnable {@Overridepublic final void onNext(T t) {......trySchedule();}final void trySchedule() {......worker.schedule(this);}}
}

调用HandlerScheduler的createWorker()返回HandlerWorker()

final class HandlerScheduler extends Scheduler {@Overridepublic Worker createWorker() {return new HandlerWorker(handler, async);}
}

调用HandlerScheduler.HandlerWorker的schedule()，将Runnable封装成ScheduledRunnable，调用主线程handler的sendMessageDelayed()

final class HandlerScheduler extends Scheduler {private static final class HandlerWorker extends Worker {@Overridepublic Disposable schedule(Runnable run, long delay, TimeUnit unit) {......run = RxJavaPlugins.onSchedule(run);ScheduledRunnable scheduled = new ScheduledRunnable(handler, run);Message message = Message.obtain(handler, scheduled);message.obj = this; if (async) {message.setAsynchronous(true);}handler.sendMessageDelayed(message, unit.toMillis(delay));......return scheduled;}}
}

最终主线程会调用FlowableObserveOn.BaseObserveOnSubscriber的run()，根据sourceMode判断是同步还是异步

  • FlowableObserveOn.ObserveOnSubscriber的runSync()和runAsync()都调用downstream的onNext()传递结果
public final class FlowableObserveOn<T> extends AbstractFlowableWithUpstream<T, T> {.....abstract static class BaseObserveOnSubscriber<T>extends BasicIntQueueSubscription<T>implements FlowableSubscriber<T>, Runnable {......@Overridepublic final void run() {if (outputFused) {runBackfused();} else if (sourceMode == SYNC) {runSync();} else {runAsync();}}}static final class ObserveOnSubscriber<T> extends BaseObserveOnSubscriber<T>implements FlowableSubscriber<T> {void runSync() {......final Subscriber<? super T> a = downstream;......for (;;) {......while (e != r) {......a.onNext(v);......}......}}.....@Overridevoid runAsync() {final Subscriber<? super T> a = downstream;for (;;) {......while (e != r) {.....a.onNext(v);.....}.....}}}
}

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