You can write like this

private BehaviorSubject bs; private void testSeri() { bs = BehaviorSubject.create(); //每3次 accept 一次 bs.buffer(3) .subscribe(new Consumer>() { @Override public void accept(@NonNull List ints) throws Exception { StringBuilder sb = new StringBuilder(); for (int i = 0; i < ints.size(); i++){ sb.append(ints.get(0)); } Toast.makeText(TestSubjectActivity.this, sb.toString(), Toast.LENGTH_SHORT).show(); } }); } @Override public boolean onKeyDown(int keyCode, KeyEvent event) { bs.onNext(keyCode); return super.onKeyDown(keyCode, event); }

onKeyDown is the callback of Activity. It is inconvenient to wrap it in another layer, so we use Subject, which can transmit data [anytime and anywhere], subscribe and transmit easily and write separately. For general callbacks, you can write it like this. Let me give you a feel for the callbacks positioned by Baidu

class LocationObservable implements ObservableOnSubscribe { @Override public void subscribe(final ObservableEmitter e) throws Exception { initLocation(); mLocationClient.registerLocationListener( new BDLocationListener(){ @Override public void onReceiveLocation(BDLocation location) { if (location != null) { mLocationClient.stop(); if (!TextUtils.isEmpty(location.getCity())) { e.onNext(location); e.onComplete(); } } else { // 定位失败 e.onError(new Exception("百度地图 定位失败")); } } } ); mLocationClient.start(); } }

For general functions, you can do this

Observable o1 = Observable.fromCallable(new Callable() { @Override public String call() { return func1(); } }); public String func1(){ return "ok"; }