RxJava - Subject 入門

Subject 入門
Rx Ja Night 2016 #1
2016-02-25

• 白山文彦
• 株式会社マナボ技術者

Subject とはなんだろうか？

/** 
* Represents an object that is both an Observable and an Observer. 
*/ 
public abstract class Subject<T, R> extends Observable<R> implements Observer<T> { 
protected Subject(OnSubscribe<R> onSubscribe) { 
super(onSubscribe); 
}
...
}

Observer でもあり
Observable でもある

ObserverとしてObservableをsubscribeできる

Observableとして他のObserverからsubscribeされる

PublishSubject<String> subject = PublishSubject.create(); 
 
subject.subscribe( 
val -> Log.i(TAG, val), 
error -> Log.e(TAG, error.getMessage(), error) 
); 
 
try { 
subject.onNext("FOO"); 
subject.onNext("BAR"); 
subject.onNext("BAZ"); 
subject.onCompleted(); 
} catch (Exception e) { 
subject.onError(e); 
}

 
); 
 
try { 
}
create

 
); 
 
try { 
}
subscribe

 
); 
 
try { 
}
bypass

 
); 
 
try { 
}
bypass
値がObservableの外から
来ていることに注目！

HOT Observable
と呼ばれたりする

• PublishSubject
• BehaviorSubject
• AsyncSubject
• ReplaySubject

• 最も基本的なSubject
• subscribeしたObserverに後続のイベントをその
ままバイパスする

ここでsubscribeしたObserverは
3つとも受け取る

ここでsubscribeしたObserverはこの１つだけ

 
); 
 
try { 
}
observer

• 直前の値（ない場合は初期値）をキャッシュし、
Observerに即座に返すSubject
• 後続のイベントはそのままバイパスする

Observable<String> observable = Observable.just("FOO", "BAR", "BAZ");
 
BehaviorSubject<String> behaviorSubject = BehaviorSubject.create("init val"); 
observable.subscribe( 
behaviorSubject::onNext 
); 
behaviorSubject.subscribe( 
);

 
); 
);
FOO, BAR, BAZ...

 
); 
);
BAZ

• Subject#onCompletedが呼ばれたらその直前の
onNext(T)をObserverに1回だけ渡す
• Subject#onNextが何度呼ばれてもonCompleted
まではObserverには何も渡らない
• REST通信など、onNext, onCompletedが1セッ
トみたいなケースで便利そう

Observable<String> sourceObservable = Observable.just("ONE"); 
AsyncSubject<String> asyncSubject = AsyncSubject.create(); 
sourceObservable.subscribe( 
data -> { 
asyncSubject.onNext(data); 
asyncSubject.onCompleted(); 
}, 
); 
 
asyncSubject.subscribe( 
data -> Log.i(TAG, data), 
);

Observable<String> sourceObservable = Observable.just("ONE"); 
AsyncSubject<String> asyncSubject = AsyncSubject.create(); 
data -> { 
asyncSubject.onNext(data); 
asyncSubject.onCompleted(); 
}, 
); 
 
asyncSubject.subscribe( 
);
ONE

• subscribeしたObservableから送出された値をす
べてキャッシュし、Observerがsubscribeしてき
たらそれをすべて渡すようなSubject
• 後続のイベントもそのままバイパスする

Observable<String> sourceObservable
= Observable.just("ONE", "TWO", "THREE", "FOUR", "FIVE"); 
ReplaySubject<String> replaySubject = ReplaySubject.create(); 
replaySubject::onNext 
); 
 
replaySubject.subscribe( 
);

); 
 
);
cache

); 
 
);
ONE, TWO, THREE, FOUR, FIVE

public class RxEventBus { 
private final Subject<Object, Object> bus
= new SerializedSubject<>(PublishSubject.create()); 
 
public void post(Object event) { 
bus.onNext(event); 
} 
 
public <T> Subscription subscribe(Class<T> clazz, Action1<T> onNext) { 
return bus.ofType(clazz).subscribe(onNext); 
} 
}

 
} 
 
} 
}
Thread Safe Subject

 
} 
 
} 
}
bypass

public class BusProvider { 
private static final RxEventBus eventBus = new RxEventBus(); 
 
private BusProvider() { 
} 
 
public static RxEventBus getInstance() { 
return eventBus; 
} 
} 
Singleton

public class ItemSelectEvent { 
private int position; 
 
public ItemSelectEvent(int position) { 
this.position = position; 
} 
 
public int getPosition() { 
return position; 
} 
} 
Simple Event

public class Adapter extends RecyclerView.Adapter<ViewHolder> { 
private LayoutInflater layoutInflater; 
private List<String> texts; 
 
public Adapter(Context context) { 
layoutInflater = LayoutInflater.from(context); 
texts = new ArrayList<>(); 
texts.add("あああああああああああ"); 
... 
} 
 
@Override 
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
View v = layoutInflater.inflate(R.layout.list_item, parent, false); 
ViewHolder viewHolder = new ViewHolder(v); 
viewHolder.itemView.setOnClickListener(view -> { 
int position = viewHolder.getAdapterPosition(); 
if (position != RecyclerView.NO_POSITION) { 
BusProvider.getInstance().post(new ItemSelectEvent(position)); 
} 
}); 
return viewHolder; 
} 
 
@Override 
public void onBindViewHolder(ViewHolder holder, int position) { 
holder.bind(texts.get(position)); 
} 
 
@Override 
public int getItemCount() { 
return texts.size(); 
} 
}

public class Adapter extends RecyclerView.Adapter<ViewHolder> { 
private LayoutInflater layoutInflater; 
private List<String> texts; 
 
public Adapter(Context context) { 
layoutInflater = LayoutInflater.from(context); 
texts = new ArrayList<>(); 
texts.add("あああああああああああ"); 
... 
} 
 
@Override 
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
View v = layoutInflater.inflate(R.layout.list_item, parent, false); 
ViewHolder viewHolder = new ViewHolder(v); 
viewHolder.itemView.setOnClickListener(view -> { 
int position = viewHolder.getAdapterPosition(); 
if (position != RecyclerView.NO_POSITION) { 
BusProvider.getInstance().post(new ItemSelectEvent(position)); 
} 
}); 
return viewHolder; 
} 
 
@Override 
public void onBindViewHolder(ViewHolder holder, int position) { 
holder.bind(texts.get(position)); 
} 
 
@Override 
public int getItemCount() { 
return texts.size(); 
} 
}
ottoとほぼ同じ！

public class MainActivity extends AppCompatActivity { 
private static final String TAG = MainActivity.class.getSimpleName(); 
 
@Bind(R.id.recycler_view) 
RecyclerView recyclerView; 
 
private Subscription subscription; 
 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 
ButterKnife.bind(this); 
 
recyclerView.setLayoutManager(new LinearLayoutManager(this)); 
recyclerView.setHasFixedSize(true); 
recyclerView.setItemAnimator(new DefaultItemAnimator()); 
recyclerView.setAdapter(new Adapter(this)); 
} 
 
 
@Override 
protected void onResume() { 
super.onResume(); 
subscription = BusProvider.getInstance().subscribe( 
ItemSelectEvent.class, 
e -> Toast.makeText(this, "position: " + e.getPosition(), Toast.LENGTH_SHORT).show() 
); 
} 
 
@Override 
protected void onPause() { 
subscription.unsubscribe(); 
super.onPause(); 
} 
}

public class MainActivity extends AppCompatActivity { 
private static final String TAG = MainActivity.class.getSimpleName(); 
 
@Bind(R.id.recycler_view) 
RecyclerView recyclerView; 
 
private Subscription subscription; 
 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 
ButterKnife.bind(this); 
 
recyclerView.setLayoutManager(new LinearLayoutManager(this)); 
recyclerView.setHasFixedSize(true); 
recyclerView.setItemAnimator(new DefaultItemAnimator()); 
recyclerView.setAdapter(new Adapter(this)); 
} 
 
 
@Override 
protected void onResume() { 
super.onResume(); 
subscription = BusProvider.getInstance().subscribe( 
ItemSelectEvent.class, 
e -> Toast.makeText(this, "position: " + e.getPosition(), Toast.LENGTH_SHORT).show() 
); 
} 
 
@Override 
protected void onPause() { 
subscription.unsubscribe(); 
super.onPause(); 
} 
}
ここもそっくり！

https://github.com/srym/RxEventBus

RxJava - Subject 入門

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