代码一：
observable.subscribeOn(Schedulers.io())
.map(new ResultFunc<Observable>())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(spSubscriber);
map会调用以下方法，mapper参数就是new ResultFunc<Observable>(),RxJavaPlugins.onAssembly(new ObservableMap<T, R>(this, mapper))这句话中的this,就是代码一中的observablesubscribeOn,
代码二 ：
@CheckReturnValue
@SchedulerSupport(SchedulerSupport.NONE)
public final <R> Observable<R> map(Function<? super T, ? extends R> mapper) {
ObjectHelper.requireNonNull(mapper, "mapper is null");
return RxJavaPlugins.onAssembly(new ObservableMap<T, R>(this, mapper));
}
把this,对象保存为source,并注册了function函数
代码三：
public ObservableMap(ObservableSource<T> source, Function<? super T, ? extends U> function) {
super(source);
this.function = function;
}
然后执行代码一中的subscribe方法，进行观察者注册,
代码四：在subscribe方法中会调用subscribeActual(observer)方法，这个方法是父类的抽象方法，因为当前的子类为ObservableMap,所以会去调用
代码五
@SchedulerSupport(SchedulerSupport.NONE)
@Override
public final void subscribe(Observer<? super T> observer) {
ObjectHelper.requireNonNull(observer, "observer is null");
try {
observer = RxJavaPlugins.onSubscribe(this, observer);
ObjectHelper.requireNonNull(observer, "Plugin returned null Observer");
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;
}
}
在代码五中，source会去注册source的subscribe,因为代码四中的subscribe是ObservableMap的(这个地方有疑问),这个source就是代码一中的observable,这样子就把代码五中包装一层new MapObserver<T, U>(t, function)的又成功注册给了source,当source发出onNext时，就会先触发MapObserver的onNext
代码五：
@Override
public void subscribeActual(Observer<? super U> t) {
source.subscribe(new MapObserver<T, U>(t, function));
}
在MapObserver的onNext方法中会去调用转换方法mapper.apply(t),并且把转换后的结果v返回,最后在调用代码一中的 spSubscriber方法，实现了结果调用。
代码六：
@Override
public void onNext(T t) {
if (done) {
return;
}
if (sourceMode != NONE) {
actual.onNext(null);
return;
}
U v;
try {
v = ObjectHelper.requireNonNull(mapper.apply(t), "The mapper function returned a null value.");
} catch (Throwable ex) {
fail(ex);
return;
}
actual.onNext(v);
}
完。