首先从一段代码开始Observable.create(new ObservableOnSubscribe<Integer>() {
@Override
public void subscribe(ObservableEmitter<Integer> emitter) throws Exception {
emitter.onNext(1);
emitter.onComplete()
}
}).subscribe(new Observer<Integer>() {
@Override
public void onSubscribe(Disposable d) {
}
@Override
public void onNext(Integer integer) {
}
@Override
public void onError(Throwable e) {
}
@Override
public void onComplete() {
}
});; 进入看Observable.creat方法
public static <T> Observable<T> create(ObservableOnSubscribe<T> source) {
ObjectHelper.requireNonNull(source, "source is null");
return RxJavaPlugins.onAssembly(new ObservableCreate<T>(source));
}这里生成了一个ObservableCreate<T>(source)了继续看下继续看RxJavaPlugins.onAssembly方法
public static <T> Observable<T> onAssembly(@NonNull Observable<T> source) {
Function<? super Observable, ? extends Observable> f = onObservableAssembly;
if (f != null) {
return apply(f, source);
}
return source;
}接下来看下onObservableAssembly
static volatile Function<? super Observable, ? extends Observable> onObservableAssembly;
public static void setOnObservableAssembly(@Nullable Function<? super Observable, ? extends Observable> onObservableAssembly) {
if (lockdown) {
throw new IllegalStateException("Plugins can't be changed anymore");
}
RxJavaPlugins.onObservableAssembly = onObservableAssembly;
}因为setOnObservableAssembly()方法只有在rxJavaPlugins的reset（）方法里面设置为null为没有其他设置，所以这个方法就是返回source参数ObservableCreate对象。
以上知道create方法就是生成了一个 ObservableCreate对象现在create方法看完了。接下来看subscribe()方法
public final void subscribe(Observer<? super T> observer) {
ObjectHelper.requireNonNull(observer, "observer is null");
try {
observer = RxJavaPlugins.onSubscribe(this, observer); 1
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); 2
} 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;
}
} 1处是把observer返回
接下来看2处
protected abstract void subscribeActual(Observer<? super T> observer);这是抽象方法,子类是刚刚的create()方法的创建的ObservableCreate类
接下来看下这类的subscribeActual方法
protected void subscribeActual(Observer<? super T> observer) {
CreateEmitter<T> parent = new CreateEmitter<T>(observer);1
observer.onSubscribe(parent);2
try {
source.subscribe(parent);3
} catch (Throwable ex) {
Exceptions.throwIfFatal(ex);
parent.onError(ex);
}
}首先1处创建了一个CreateEmitter 在rxjava中每个方法几乎都会创建自己的Emitter对象接下来看看这类的声明
static final class CreateEmitter<T>
extends AtomicReference<Disposable>
implements ObservableEmitter<T>, Disposable {}这个类是ObservableEmitter的子类 接下来执行2 即observer的onSubscribe()方法 接下来3 在下面可知source是ObservableOnSubscribe对象
public final class ObservableCreate<T> extends Observable<T> {
final ObservableOnSubscribe<T> source;
public ObservableCreate(ObservableOnSubscribe<T> source) {
this.source = source;
}
}
在最上面一段代码中可以看到，我们在Create（）方法参数的subscribe()回调中调用了emitter.onNext(1) emitter.onComplete()方法
接下来看下CreateEmitter的onNext方法
@Override
public void onNext(T t) {
if (t == null) {
onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
return;
}
if (!isDisposed()) {
observer.onNext(t);
}
}在这方法中，直接调用了Observer 的onNext方法。
这样一套Create() 和 Subscribe()方法的流程就走完了
