Why is OnComplete not called in this code? (RxAndroid)

Question

I know OnComplete of a Observer is called when all the items are emitted. In the below code, I am putting data from a cursor to an ArrayList in a flatMap operator. My cursor has 100 entries ( c.getCount() gives 100 ) and the size of my list is 100. The onNext is called 100 times too. But the onComplete is not called. I am populating a listview in onComplete.

static int i = 0;
final List<String> ar = new ArrayList<>();
ListView lv = ...;
ArrayAdapter<String> adapter = ...;   
.
.
. 
q.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread())
                    .flatMap(new Func1<SqlBrite.Query, Observable<String>>() {
                @Override
                public Observable<String> call(SqlBrite.Query query) {
                    Cursor c = query.run();
                    c.moveToFirst();
                    Log.d("testApp", String.valueOf(c.getCount())); // prints 100
                    do {
                        ar.add(c.getString(0));
                    } while (c.moveToNext());
                    Log.d("testApp", String.valueOf(ar.size())); // prints 100
                    return Observable.from(ar);
                }
            }).subscribe(new Observer<String>() {
                @Override
                public void onCompleted() {
                    Log.d("testApp", "onComplete called");
                    lv.setAdapter(adapter);
                }

            @Override
            public void onError(Throwable e) {
            }

            @Override
            public void onNext(String s) {
                Log.d("testApp", "onNext called " + String .valueOf(++i) + " with " + s); // printed 100 times
                adapter.add(s);
            }
        });

The new stream of Observable is to complete after 100 but it does not.

Any help is appreciated, Thank You

My guess is that you do IO on the android main thread and since you don't do anything in onError, you don't see the exception. Put the observeOn just before the subscribe. — akarnokd
And never, NEVER, leave onError empty - in the time I have spent searching for errors because of an empty onError I could write e.printStackTrace() more than enough times for a programmer life... — david.mihola

dwursteisen dwursteisen · Accepted Answer · 2015-07-09T18:45:54

FlatMap operator merge your main stream with your flatMapped stream. Your observable will complete if q and your Observable from your array complete. So check why q doesn't no complete.

Why is OnComplete not called in this code? (RxAndroid)

1 Answers