RxAppBarLayout for observing AppBarLayout vertical offset

RxAppBarLayout.java

import android.support.design.widget.AppBarLayout;

import rx.Observable;
import rx.Subscriber;
import rx.Subscription;

/**
 * Helper class for creating Observable of AppBarLayout visibility.
 * Can be easily modified to return Integer values, if one needs to user verticalOffset param directly.
 * See for further info: http://stackoverflow.com/questions/30779667/android-collapsingtoolbarlayout-and-swiperefreshlayout-get-stuck
 */
public final class RxAppBarLayout {

    public static Observable<Boolean> appBarVisibility(AppBarLayout appBarLayout) {
        return Observable.create(new AppBarLayoutStateOnSubscribe(appBarLayout));
    }

    private static class AppBarLayoutStateOnSubscribe implements Observable.OnSubscribe<Boolean> {

        private final android.support.design.widget.AppBarLayout appBarLayout;
        private Boolean mAppBarVisible = true;

        private AppBarLayoutStateOnSubscribe(AppBarLayout appBarLayout) {
            this.appBarLayout = appBarLayout;
        }

        @Override
        public void call(Subscriber<? super Boolean> subscriber) {
            AppBarLayout.OnOffsetChangedListener listener = new AppBarLayout.OnOffsetChangedListener() {
                @Override
                public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
                    mAppBarVisible = verticalOffset == 0;
                    subscriber.onNext(mAppBarVisible);
                }
            };
            appBarLayout.addOnOffsetChangedListener(listener);
            subscriber.add(new Subscription() {
                @Override
                public void unsubscribe() {
                    appBarLayout.removeOnOffsetChangedListener(listener);
                }

                @Override
                public boolean isUnsubscribed() {
                    return false;
                }
            });
            subscriber.onNext(mAppBarVisible);
        }
    }

}