RxJava源码解析02-订阅过程

RxJava源码解析-订阅过程

以最简单的调用过程为例

Observable.create(new Observable.OnSubscribe<String>() {
    @Override
    public void call(Subscriber<? super String> subscriber) {
        subscriber.onNext("hello");
        subscriber.onNext("world");
        subscriber.onCompleted();
    }
}).subscribe(new Subscriber<String>() {
    @Override
    public void onCompleted() {

    }

    @Override
    public void onError(Throwable e) {

    }

    @Override
    public void onNext(String s) {

    }  
}  

create()

先来看create()

public static <T> Observable<T> create(OnSubscribe<T> f) {
    return new Observable<T>(RxJavaHooks.onCreate(f));
}  

此处RxJavaHooks.onCreate(f)返回的就是OnSubscribe对象，然后作为传参传入Observable并返回。

//Observable
protected Observable(OnSubscribe<T> f) {
    this.onSubscribe = f;
}

即create会将f赋值给Observable.onSubscribe，并返回Observable对象

subscribe()

再来看subscribe

public final Subscription subscribe(Subscriber<? super T> subscriber) {
    return Observable.subscribe(subscriber, this);
}  

static <T> Subscription subscribe(Subscriber<? super T> subscriber, Observable<T> observable) {
    subscriber.onStart();
    //...
    RxJavaHooks.onObservableStart(observable, observable.onSubscribe).call(subscriber);
    return RxJavaHooks.onObservableReturn(subscriber);
}  

此处首先会调用subscriber.onStart()，
接着RxJavaHooks.onObservableStart一般实际返回的就是observable.onSubscribe，
然后调用observable.onSubscribe.call()，
最后通过RxJavaHooks.onObservableReturn返回Subscription对象。(也就是subscriber，Subscriber实现了Subscription接口)

总结

Observable.subscribe()的过程其实就是先调用subscriber.onStart()，再通过Observable.OnSubscribe.call(subscriber)来间接调用subscriber的onNext、onError、onCompleted等方法。call的具体实现各个OnSubscribe是不同的。

Observable.create(new Observable.OnSubscribe<String>() {
    @Override
    public void call(Subscriber<? super String> subscriber) {
        subscriber.onNext("hello world");
        subscriber.onNext("tttt");
        subscriber.onCompleted();
    }
})