先看一小段代码
Observable observable = Observable.create(observer->{
observer.onNext("处理的数字是"+Math.random()*100);
observer.onComplete();
});
observable.subscribe(consumer->{
System.out.println("我处理的元素是"+consumer);
});
observable.subscribe(consumer->{
System.out.println("我处理的元素是"+consumer);
});
执行结果是
我处理的元素是处理的数字是19.702425673460567
我处理的元素是处理的数字是9.601318081392996
先看Observable.create方法
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static Observable create(ObservableOnSubscribe source) {
ObjectHelper.requireNonNull(source, "source is null");
return RxJavaPlugins.onAssembly(new ObservableCreate(source));
}
参数是ObservableOnSubscribe
public interface ObservableOnSubscribe {
/**
* Called for each Observer that subscribes.
* @param emitter the safe emitter instance, never null
* @throws Exception on error
*/
void subscribe(@NonNull ObservableEmitter emitter) throws Exception;
}
其实我们可以把我们最开始的例子改写成
ObservableOnSubscribe observableOnSubscribe = new ObservableOnSubscribe(){
@Override
public void subscribe(ObservableEmitter emitter) throws Exception {
emitter.onNext("处理的数字是"+Math.random()*100);
emitter.onComplete();
}};
Observable observable = Observable.create(observableOnSubscribe);
observable.subscribe(consumer->{
System.out.println("我处理的元素是"+consumer);
});
observable.subscribe(consumer->{
System.out.println("我处理的元素是"+consumer);
});
我们把create方法参数还原成1.8之前的写法，我们一眼就看出文章一开始的代码写的observer是影响我们理解代码的
observer->{
observer.onNext("处理的数字是"+Math.random()*100);
observer.onComplete();
}
其实是emitter更为恰当
emitter->{
emitter.onNext("处理的数字是"+Math.random()*100);
emitter.onComplete();
}
这个ObservableEmitter 又是个接口，也就是说下面这几行代码只是定义了一个模版，subscribe的时候，由ObservableEmitter的实现类还具体执行onNext和onComplete。那么实现类在哪里呢？
ObservableOnSubscribe observableOnSubscribe = new ObservableOnSubscribe(){
@Override
public void subscribe(ObservableEmitter emitter) throws Exception {
emitter.onNext("处理的数字是"+Math.random()*100);
emitter.onComplete();
}};
我们再看Observable.create方法
@CheckReturnValue
@NonNull
@SchedulerSupport(SchedulerSupport.NONE)
public static Observable create(ObservableOnSubscribe source) {
ObjectHelper.requireNonNull(source, "source is null");
return RxJavaPlugins.onAssembly(new ObservableCreate(source));
}
也就是说
Observable observable = Observable.create(observableOnSubscribe);
observable等于ObservableCreate的一个实例。这个ObservableCreate留着待用。
我们再看observable.subscribe方法
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public final Disposable subscribe(Consumer onNext) {
return subscribe(onNext, Functions.ON_ERROR_MISSING, Functions.EMPTY_ACTION, Functions.emptyConsumer());
}
可以看到除了onNext函数是往下传递的，剩下的参数都是默认值。
再放下跟subscribe方法
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public final Disposable subscribe(Consumer onNext, Consumer onError,
Action onComplete, Consumer onSubscribe) {
ObjectHelper.requireNonNull(onNext, "onNext is null");
ObjectHelper.requireNonNull(onError, "onError is null");
ObjectHelper.requireNonNull(onComplete, "onComplete is null");
ObjectHelper.requireNonNull(onSubscribe, "onSubscribe is null");
LambdaObserver ls = new LambdaObserver(onNext, onError, onComplete, onSubscribe);
subscribe(ls);
return ls;
}
注意这个LambdaObserver，传递进来的onNext函数，在这里包装成了一个observer对象。
继续进入subscribe(ls);
@SchedulerSupport(SchedulerSupport.NONE)
@Override
public final void subscribe(Observer observer) {
ObjectHelper.requireNonNull(observer, "observer is null");
try {
observer = RxJavaPlugins.onSubscribe(this, observer);
ObjectHelper.requireNonNull(observer, "The RxJavaPlugins.onSubscribe hook returned a null Observer. Please change the handler provided to RxJavaPlugins.setOnObservableSubscribe for invalid null returns. Further reading: https://github.com/ReactiveX/RxJava/wiki/Plugins");
subscribeActual(observer);
} catch (NullPointerException e) { // NOPMD
throw e;
} catch (Throwable e) {
Exceptions.throwIfFatal(e);
// can't call onError because no way to know if a Disposable has been set or not
// can't call onSubscribe because the call might have set a Subscription already
RxJavaPlugins.onError(e);
NullPointerException npe = new NullPointerException("Actually not, but can't throw other exceptions due to RS");
npe.initCause(e);
throw npe;
}
}
没什么重要的，继续进入subscribeActual(observer);
protected abstract void subscribeActual(Observer observer);
发现是个抽象方法，那么自然应该是刚刚待用的ObservableCreate的
subscribeActual方法
protected void subscribeActual(Observer observer) {
CreateEmitter parent = new CreateEmitter(observer);
observer.onSubscribe(parent);
try {
source.subscribe(parent);
} catch (Throwable ex) {
Exceptions.throwIfFatal(ex);
parent.onError(ex);
}
}
第一句把observer对象再包装成一个emitter对象
第二句什么也没执行，因为observer只有onNext是传进来一个lambda，其他三个参数都是默认的。记得是个emptyConsumer。
本文的重中之重就是下面这句
source.subscribe(parent);
source就是我们一开始定义的observableOnSubscribe
subscribe就是observableOnSubscribe的subscribe方法
参数parent就是刚刚的CreateEmitter
ObservableOnSubscribe observableOnSubscribe = new ObservableOnSubscribe(){
@Override
public void subscribe(ObservableEmitter emitter) throws Exception {
emitter.onNext("处理的数字是"+Math.random()*100);
emitter.onComplete();
}};
至此所有逻辑拼接成功
先执行subscribe，然后再执行我们自己定义的onNext。
done