How to handle Item clicks for a recycler view using RxJava

Question

I was interested to find out what is the best way to respond to a item click of a recycler view.

Normally I would add a onclick() listener to the ViewHolder and pass back results to the activity/fragment through a interface.

I thought about adding a Observable in the onBindViewHolder but i do not want to create a new Observable for every item binding.

Answer 1

You can use RxBinding and then create a subject inside of your adapter, then redirect all the events to that subject and just create a getter of the subject to act as an observable and finally just subscribe you on that observable.

private PublishSubject<View> mViewClickSubject = PublishSubject.create();

public Observable<View> getViewClickedObservable() {
    return mViewClickSubject.asObservable();
}

@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup pParent, int pViewType) {
    Context context = pParent.getContext();
    View view = (View) LayoutInflater.from(context).inflate(R.layout.your_item_layout, pParent, false);
    ViewHolder viewHolder = new ViewHolder(view);

    RxView.clicks(view)
            .takeUntil(RxView.detaches(pParent))
            .map(aVoid -> view)
            .subscribe(mViewClickSubject);

    return viewHolder;
}

An usage example could be:

mMyAdapter.getViewClickedObservable()
        .subscribe(view -> /* do the action. */);

Answer 2

Step 1: Move the business logic out of the activities to domain classes/services

Optional: Use https://github.com/roboguice/roboguice to easily wire up your services with each other.

Step 2: @Inject (or just set) your service into your adapter

Step 3: Grab https://github.com/JakeWharton/RxBinding and use the super powers in your adapter:

RxView.clicks(button).subscribe(new Action1<Void>() {
    @Override
    public void call(Void aVoid) {
        myCoolService.doStuff();
    }
});

Step 4: Get a runtime crash and learn how to deal with subscriptions

Step 5: PROFIT :)

Answer 3

I would suggest you to do with your initial aproach of an observable per element on click, but in order to avoid create a new observable every time you can just cache the items emitted the first time using cache.

      /**
 * Here we can prove how the first time the items are delayed 100 ms per item emitted but second time becuase it´s cached we dont have any delay since 
 * the item emitted are cached
 */
@Test
public void cacheObservable() {
    Integer[] numbers = {0, 1, 2, 3, 4, 5};

    Observable<Integer> observable = Observable.from(numbers)
                                               .doOnNext(number -> {
                                                   try {
                                                       Thread.sleep(100);
                                                   } catch (InterruptedException e) {
                                                       e.printStackTrace();
                                                   }
                                               })
                                               .cache();
    long time = System.currentTimeMillis();
    observable.subscribe(System.out::println);
    System.out.println("First time took:" + (System.currentTimeMillis() - time));
    time = System.currentTimeMillis();
    observable.subscribe(System.out::println);
    System.out.println("Second time took:" + (System.currentTimeMillis() - time));

}

Answer 4

My solution was much like @epool 's except use EventBus model.

First, create a RxBus: RxBus.java

public class RxBus {
    private final Subject<Object, Object> _bus = new SerializedSubject<>(PublishSubject.create());
    public void send(Object o) { _bus.onNext(o); }
    public Observable<Object> toObserverable() { return _bus; }
    public boolean hasObservers() { return _bus.hasObservers(); }
}

Then, you have two way to use RxBus. Create your custom Application class with RxBus reference or create RxBus in Activity/Fragment then pass it to adapter. I'm use the first.

MyApp.java

public class MyApp extends Application {
    private static MyApp _instance;
    private RxBus _bus;
    public static MyApp get() {  return _instance; }

    @Override
    public void onCreate() {
        super.onCreate();
        _instance = this;
        _bus = new RxBus();
    }

    public RxBus bus() { return _bus; }
}

then use

MyApp.get().bus() 

to get RxBus instance.

The usage of RxBus in Adpater was like this:

public class MyRecyclerAdapter extends ... {
    private RxBus _bus;

    public MykRecyclerAdapter (...) {
        ....
        _bus = MyApp.get().bus();
    }

    public ViewHolder onCreateViewHolder (...) {
        _sub = RxView.longClicks(itemView)  // You can use setOnLongClickListener as the same
              .subscribe(aVoid -> {
                        if (_bus.hasObservers()) { _bus.send(new SomeEvent(...)); }
                    });      
    }
}

You can send any class with _bus.send(), which We will recieve in the Activity:

RxBus bus = MyApp.get().bus();  // get the same RxBus instance
_sub = bus.toObserverable()
            .subscribe(e -> doSomething((SomeEvent) e));

About unsubscribe.

In MyRecyclerAdapter call _sub.unsubscribe() in clearup() methods and call _sub.unsubscribe() in Activity's onDestory().

@Override
public void onDestroy() {
    super.onDestroy();
    if (_adapter != null) {
        _adapter.cleanup();
    }
    if (_sub != null) {
         _sub.unsubscribe()
    }
}

Answer 5

We generally need the Pojo/Model class from list on clicked index. I do it in following way:

1) Create a BaseRecyclerViewAdapter

abstract class BaseRecyclerViewAdapter<T> : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
    private val clickListenerPublishSubject = PublishSubject.create<T>()

    fun observeClickListener(): Observable<T> {
        return clickListenerPublishSubject
    }

    fun performClick(t: T?) {
        t ?: return
        clickListenerPublishSubject.onNext(t)
    }
}

2) In any adapter (For example MyAdapter)

class MyAdapter(private val events: List<Event>, context: Context) : BaseRecyclerViewAdapter<Event>() {
    //... Other methods of RecyclerView
    override fun onBindViewHolder(holder: RecyclerView.ViewHolder?, position: Int) {
        if (holder is EventViewHolder) {
            holder.eventBinding?.eventVm = EventViewModel(events[position])

            holder.eventBinding?.root?.setOnClickListener({ _ ->
                // This notifies the subscribers
                performClick(events[position])
            })
        }
    }
}

3) Inside the Activity or Fragment where click listener is needed

myAdapter?.observeClickListener()
                ?.subscribe({ eventClicked ->
                    // do something with clicked item

                })