This article details the basic usage of RxJava. RxJava is a magical framework with very simple usage, but the internal implementation is a bit complicated and the code logic is a bit convoluted. Online articles about RxJava source code analysis, source code posts are few and incomplete. The complete source code analysis is listed below for reference.
1. Basic usage of RxJava
Observable.create(new Observable.OnSubscribe<Object>() {
@Override
public void call(Subscriber<? super Object> subscriber) {
}
}).subscribe(new Observer<Object>() {
@Override
public void onCompleted() {
}
@Override
public void onError(Throwable e) {
}
@Override
public void onNext(Object o) {
}
});2. First look at the .subscribe(new Observer
public final Subscription subscribe(final Observer<? super T> observer) {
if (observer instanceof Subscriber) {
return subscribe((Subscriber<? super T>)observer);
}
if (observer == null) {
throw new NullPointerException("observer is null");
}
return subscribe(new ObserverSubscriber<T>(observer));
}This is just the passed in observer parameter A simple encapsulation (ObserverableSubscriber)
Continue to look at the subscribe method
public final Subscription subscribe(Subscriber<? super T> subscriber) {
return Observable.subscribe(subscriber, this);
} static <T> Subscription subscribe(Subscriber<? super T> subscriber, Observable<T> observable) {
// validate and proceed
if (subscriber == null) {
throw new IllegalArgumentException("subscriber can not be null");
}
if (observable.onSubscribe == null) {
throw new IllegalStateException("onSubscribe function can not be null.");
/*
* the subscribe function can also be overridden but generally that's not the appropriate approach
* so I won't mention that in the exception
*/
}
// new Subscriber so onStart it
subscriber.onStart();
/*
* See https://github.com/ReactiveX/RxJava/issues/216 for discussion on "Guideline 6.4: Protect calls
* to user code from within an Observer"
*/
// if not already wrapped
if (!(subscriber instanceof SafeSubscriber)) {
// assign to `observer` so we return the protected version
subscriber = new SafeSubscriber<T>(subscriber);
}
// The code below is exactly the same an unsafeSubscribe but not used because it would
// add a significant depth to already huge call stacks.
try {
// allow the hook to intercept and/or decorate
RxJavaHooks.onObservableStart(observable, observable.onSubscribe).call(subscriber);
return RxJavaHooks.onObservableReturn(subscriber);
} catch (Throwable e) {
// special handling for certain Throwable/Error/Exception types
Exceptions.throwIfFatal(e);
// in case the subscriber can't listen to exceptions anymore
if (subscriber.isUnsubscribed()) {
RxJavaHooks.onError(RxJavaHooks.onObservableError(e));
} else {
// if an unhandled error occurs executing the onSubscribe we will propagate it
try {
subscriber.onError(RxJavaHooks.onObservableError(e));
} catch (Throwable e2) {
Exceptions.throwIfFatal(e2);
// if this happens it means the onError itself failed (perhaps an invalid function implementation)
// so we are unable to propagate the error correctly and will just throw
RuntimeException r = new OnErrorFailedException("Error occurred attempting to subscribe [" + e.getMessage() + "] and then again while trying to pass to onError.", e2);
// TODO could the hook be the cause of the error in the on error handling.
RxJavaHooks.onObservableError(r);
// TODO why aren't we throwing the hook's return value.
throw r; // NOPMD
}
}
return Subscriptions.unsubscribed();
}
}You only need to pay attention here
RxJavaHooks.onObservableStart(observable, observable.onSubscribe).call(subscriber);
public static <T> Observable.OnSubscribe<T> onObservableStart(Observable<T> instance, Observable.OnSubscribe<T> onSubscribe) {
Func2<Observable, Observable.OnSubscribe, Observable.OnSubscribe> f = onObservableStart;
if (f != null) {
return f.call(instance, onSubscribe);
}
return onSubscribe;
}RxJavaHooks.onObservableStart(observable, observable.onSubscribe) 这个方法返回的是它的第二个参数，也就是Observable它自己的onSubscribe 对象， 所以在subscribe 方法里面调用了 onSubscribe.call(subscriber)方法
The subscriber here is the parameter passed in
protected Observable(OnSubscribe<T> f) {
this.onSubscribe = f;
}public static <T> Observable<T> create(OnSubscribe<T> f) {
return new Observable<T>(RxJavaHooks.onCreate(f));
}It can be seen that the onSubscribe object is the parameter passed in by create, then the whole process is very clear
The entire process will only be executed when the subscribe method is called: subscribe ===>Call onSubscribe.call(observer ) method also passes the observer in
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