Don't break the chain: use RxJava's compose() operator -> Android + Retrolambda + Observable.Transformer cannot find symbol method

README.md

Problem

Error:(29, 37) error: cannot find symbol method subscribeOn(Scheduler)

This happens compiling this code borrowed from http://blog.danlew.net/2015/03/02/dont-break-the-chain/#comment-2388677116

final Observable.Transformer schedulersTransformer =
            observable -> observable.subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread());

Environment

• Android Studio 2.0
• Retrolambda
• Compiled with Java 8

RxUtils.java

import rx.Observable;
import rx.Subscription;
import rx.android.schedulers.AndroidSchedulers;
import rx.schedulers.Schedulers;

public class RxUtil {
    /**
     * {@link rx.Observable.Transformer} that transforms the source observable to subscribe in the
     * io thread and observe on the Android's UI thread.
     */
    private static Observable.Transformer ioToMainThreadSchedulerTransformer;

    static {
        ioToMainThreadSchedulerTransformer = createIOToMainThreadScheduler();
    }

    /**
     * Get {@link rx.Observable.Transformer} that transforms the source observable to subscribe in
     * the io thread and observe on the Android's UI thread.
     *
     * Because it doesn't interact with the emitted items it's safe ignore the unchecked casts.
     *
     * @return {@link rx.Observable.Transformer}
     */
    @SuppressWarnings("unchecked")
    private static <T> Observable.Transformer<T, T> createIOToMainThreadScheduler() {
        return tObservable -> tObservable.subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread());
    }

    @SuppressWarnings("unchecked")
    public static <T> Observable.Transformer<T, T> applyIOToMainThreadSchedulers() {
        return ioToMainThreadSchedulerTransformer;
    }
}

UseExample.java

            ApiService.getInstance().apiCall(parameter)
                    .compose(RxUtil.applyIOToMainThreadSchedulers())
                    .subscribe(data -> {});
            

If you Replace lambda with anonymous class (ALT + ENTER in Intellij), you'll see this:

        @Override public Object call(Object observable) {
        return observable.subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread());
    }

And you'd see, that Object indeed has not subscribeOn() method. Casting observable to Observable and replacing with lambda gives this:

observable -> ((Observable) observable).subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread());

Which compiles successfully.

Same configuration as you, this is working for me:

private final Observable.Transformer<Object, Object> mSchedulersTransformer;

Later...

mSchedulersTransformer = observable -> observable .subscribeOn(postThread.get()) .observeOn(mainThread.get());

Finally...

@SuppressWarnings("unchecked") protected <T> Transformer<T, T> applySchedulers() { return (Transformer<T, T>) mSchedulersTransformer; }

I did ((Observable) observable).subscribeOn(Schedulers.io()) and it worked

Observable.Transformer<Observable, Observable> schedulersTransformer = observable -> observable.subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); worked for me