LoginActivity.java

class LoginActivity extends Activity {
    // Setup stuff
    
    @Override
    public void onResume() {
        // Subscribe to the login view submit
        AppObservable.bindActivity(this, loginView.getUserCredentialsObservable().subscribeOn(mainThread()))
            .doOnNext(loginView.showProgress(true))
            .flatMap(creds -> getTokenObservable(creds))
            .subscribe(this::handleSuccess)
    }
    
    private Observable<Token> getTokenObservable(UserCredentials userCredentials) {
        return apiService.getAuthToken(userCredentials)
            .observeOn(mainThread())
            .onErrorResume(throwable -> {
                if (throwable instanceof RetrofitError) {
                    handleRetrofitError((RetrofitError) throwable);
                    return new Token(null, null);
                }
                loginView.showProgress(false);
                return Observable.error(throwable);
            })
            .filter(token -> {
                loginView.showProgress(false);
                return !TextUtils.isEmpty(token.getAuthToken());
            })
            .doOnNext(token -> token.setUserName(userCredentials.getEmail()));
    }
}

LoginView.java

class LoginView extends LinearLayout {
    // constructors and stuff
    
    public getUserCredentialsObservable() {
        return ViewObservable.clicks(submitButton).map(onClickEvent -> getUserCredentials());
    }
    
    public UserCredentials getUserCredentials() {
        emailField.setError(null);
        passwordField.setError(null);
        Observable.combineLatest(validEmail(), validPassword(), UserCredentials::new);
    }
    
    public Observable<String> validEmail() {
        return Observable.just(emailField.getText().toString())
            .filter(email -> {
                if (TextUtils.isEmpty(email) || !email.contains("@")) {
                    emailField.setError("Invalid email.");
                    return false;
                }
                return true;
            });
    }
    
    public Observable<String> validPassword() {
        return Observable.just(passwordField.getText().toString())
            .filter(password -> {
                if (password.length() < 6) {
                    passwordField.setError("Invalid password.");
                    return false;
                }
                return true;
            });
    }
}