之前在学习Rxjava时，写demo。发现在FlatMap运算中，即使上游发送了onComplete，在下游也无法执行onComplete：

        Observable
                .create(new ObservableOnSubscribe<Integer>() {
                    @Override
                    public void subscribe(ObservableEmitter<Integer> e) throws Exception {
//                        Log.i(TAG, "!!!!onNext 1 before");
//                        e.onNext(1);
//                        Log.i(TAG, "!!!!onNext 1 after");

                        Log.i(TAG, "!!!!onNext 2 before");
                        e.onNext(2);
                        Log.i(TAG, "!!!!onNext 2 after");

                        // 位置1：如果注释以下代码，在位置10出将无法触发
                        Log.i(TAG, "!!!!onComplete before");
                        e.onComplete();
                        Log.i(TAG, "!!!!onComplete after");
                    }
                })
                .flatMap(new Function<Integer, ObservableSource<String>>() {
                    @Override
                    public ObservableSource<String> apply(final Integer integer) throws Exception {
                        Log.i(TAG, "@@@@flatMap " + integer);
                        Observable<String> ob = Observable
                                .create(new ObservableOnSubscribe<String>() {
                                    @Override
                                    public void subscribe(final ObservableEmitter<String> e) throws Exception {
                                        String value = "####flatMap: Observable2,create: " + integer;
                                        Log.i(TAG,value);
                                        Log.i(TAG, "####flatMap: Observable2, next " + integer + " before");
                                        e.onNext(value);
                                        Log.i(TAG, "####flatMap: Observable2, next " + integer + " after");

                                        if(integer == 2){
                                            // 位置2：如果注释以下代码，在位置10出将无法触发
//                                            Log.i(TAG, "####flatMap: Observable2, onComplete 2 before");
//                                            e.onComplete();
//                                            Log.i(TAG, "####flatMap: Observable2, onComplete  2 after");
                                        }
                                    }
                                });
                        return ob;
                    }
                })
                .subscribe(new Consumer<String>() {
                    @Override
                    public void accept(String s) throws Exception {
                        Log.i(TAG, "XXXXsubscribe:" + s);
                    }
                }, new Consumer<Throwable>() {
                    @Override
                    public void accept(Throwable throwable) throws Exception {
                        Log.i(TAG, "TTTTerror");
                    }
                }, new Action() {
                    @Override
                    public void run() throws Exception {
                        //位置10：触发onComplete .如果注释位置1和位置2中任何一处，都将无法触发这里
                        Log.i(TAG, "VVVVcomplete");
                    }
                }
                );

Log.i(TAG, "VVVVcomplete"); 没有执行

为什么？？？

分析Flatmap运算符源码，主要是ObservableFlatMap 这个类：

关键类：MergeObserver，InnerObserver
关键方法：mergeObserver.onNext(),merge.onComplete(),mergeObserver.drain(),merge.insertInnser(),merge.removeInner();
innerObserver.onComplete(),

mergeObserver.drain()关键代码：

• 当innerObserver中触发了onComplete，将移除innerObserver

  
  
  QQ图片20171230235242.png

• 当mergeObserver.onComplete或onError被触发，done置为true，并且没有innerObserver时，才能触发child.onComplete()

  
  
  QQ图片20171230235250.png

innserObserver.onComplete(),onError()

QQ图片20171230235254.png