SignUpActivity.java

Func1<OnTextChangeEvent, Boolean> isNotEmpty = t -> t.text().length() != 0;
            rx.Observable.combineLatest(
                    WidgetObservable.text(mNameTextView).map(isNotEmpty),
                    WidgetObservable.text(mCompanyTextView).map(isNotEmpty),
                    WidgetObservable.text(mTitleTextView).map(isNotEmpty),
                    (a, b, c) -> a && b && c
            ).subscribe(result -> {
                        Button btn = ((SignUpActivity) getActivity()).mDoneBtn;
                        if (result) {
                            btn.getBackground().setColorFilter(getResources().getColor(R.color.accent), PorterDuff.Mode.MULTIPLY);
                        } else {
                            btn.getBackground().clearColorFilter();
                        }
                        btn.setEnabled(result);
                    }
            );

            Observable.combineLatest(
                    WidgetObservable.text(mNameTextView).map(isNotEmpty),
                    Observable.create(new Observable.OnSubscribe<Boolean>() {
                        @Override
                        public void call(final Subscriber<? super Boolean> subscriber) {
                            mNameTextView.setOnFocusChangeListener((v, hasFocus) -> {
                                if (subscriber.isUnsubscribed()) return;
                                subscriber.onNext(hasFocus);
                            });
                        }
                    }),
                    (a, b) -> a && b ? View.VISIBLE : View.INVISIBLE
            ).subscribe(
                    mNameClearBtn::setVisibility
            );