Course.java

// Assuming we have this state:
courseId

// Assuming we have these view related stuff:
refreshButton
courseCodeLabel
courseTitleLabel
sectionsAdapter // ArrayAdapter
sectionSpinner

// Fetch the course info when the observable is first subscribed,
// and subsequently when refreshes are requested.
//
// The result is cached, so that subscriptions share the latest
// fetched results and would not unnecessarily trigger network requests.
//
// P.S. `RxView.clicks` is from RxBinding.
Observable<Course> course = RxView.clicks(refreshButton)
  .startWith(null)
  // `fetchCourse` is a `(CourseId) => Course` function.
  .concatMap(new Func1<Void, Course>() {
   @Override public void call(Void a) {
     return fetchCourse(courseId);
   }
  })
  // We care about only the latest fetched result.
  .cache(1)

// Basic bindings: Course code and course title
course.subscribe(new Action1<Course>() {
   @Override public void call(Course course) {
       courseCodeLabel.setText(course.code);
       courseTitleLabel.setText(course.title);
   }
})
  
// Advanced bindings: Filtered collection
// Let's assume there is one selection at a time only, since
// this is what Spinner supports.
//
// P.S. `RxAdapterView` is from RxBinding.
RxAdapterView.itemSelections(sectionSpinner)
   // Assume `0` means "all".
   .startWith(0)
   // For every value we get from the upstream, pair it with
   // the latest `Course` instance cached by `course`.
   .withLatestFrom(course)
   .map(new Func2<Int, Course, List<Section>>() {
     @Override public void call(Int selection, Course course) {
       return Course.filterSection(course, selection);
     }
   })
   .subscribe(new Action1<List<Section>>() {
     @Override public void call(List<Section> sections) {
       sectionsAdapter.clear();
       sectionsAdapter.addAll(sections);
     }
   })