how to add data obtained in OnComplete to ArrayList

Question

final ArrayList<String> users = new ArrayList<>(); for ( VKApiDialog msg : list) { final String[] result = new String[1]; final int id=msg.message.user_id; VKRequest request1 = VKApi.users().get(VKParameters.from(VKApiConst.USER_IDS,String.valueOf(msg.message.user_id),VKApiConst.FIELDS, "first_name, last_name")); request1.executeWithListener(new VKRequest.VKRequestListener() { @Override public void onComplete(VKResponse response) { super.onComplete(response); user = ((VKList) response.parsedModel); result[0] =user.getById(id).toString(); } }); users.add(result[0]); }

after exiting onComplete variable becomes null

if users.add(result[0]) called inside, then when I call onComplete from outside, after users.size() I get 0.

`

  for ( VKApiDialog msg : list) { final String[] result = new String[1]; final int id=msg.message.user_id; VKRequest request1 = VKApi.users().get(VKParameters.from(VKApiConst.USER_IDS,String.valueOf(msg.message.user_id),VKApiConst.FIELDS, "first_name, last_name")); request1.executeWithListener(new VKRequest.VKRequestListener() { @Override public void onComplete(VKResponse response) { super.onComplete(response); user= ((VKList) response.parsedModel); result[0] =user.getById(id).toString(); users.add(result[0]); } }); System.out.println(users.size());`

Result:

04-12 13:50:00.792 11984-11984/com.example.belzik.messagefromvk I/System.out: 0 04-12 13:50:00.793 11984-11984/com.example.belzik.messagefromvk I/System.out: 0 04-12 13:50:00.793 11984-11984/com.example.belzik.messagefromvk I/System.out: 0 04-12 13:50:00.793 11984-11984/com.example.belzik.messagefromvk I/System.out: 0

You will see under debugging that users.add (result [0]) is executed first;
Tried it, from outside, onComplete called after this users.getSize() , received 0
@ kalugin1912, are you sure you called users.getSize() after VKRequestListener worked?

Answer 1 · 2016-04-12T10:45:36

If I understand everything correctly, VKRequestListener working asynchronously and you want to wait for it to run for all msg . To do this, you need to independently implement synchronization between the main thread and asynchronous callbacks. You can use CountDownLatch . It works like this:

You create something like a counter with an initial value equal to the number of expected events.
The main thread waits for the counter to reach zero before continuing.
In each asynchronous event listener, in case of success and in case of an error, we reduce the counter by one.

It looks like this:

 final List<String> users = Collections.synchronizedList(new ArrayList<>()); final CountDownLatch latch = new CountDownLatch(list.size()); // наш счетчик for ( VKApiDialog msg : list) { final int id=msg.message.user_id; VKRequest request1 = VKApi.users().get(VKParameters.from(VKApiConst.USER_IDS,String.valueOf(msg.message.user_id),VKApiConst.FIELDS, "first_name, last_name")); request1.executeWithListener(new VKRequest.VKRequestListener() { @Override public void onComplete(VKResponse response) { super.onComplete(response); user = ((VKList) response.parsedModel); users.add(user.getById(id).toString()); latch.countDown(); // уменьшаем при успехе } @Override public void onError(VKError error) { latch.countDown(); // при неудаче тоже уменьшаем } }); } latch.await(); // основной поток будет ждать здесь // тут уже можно вызвать users.getSize()

Examples of application CountDownLatch in Android is in the official documentation .

It is necessary (if necessary) to use Collections.synchronizedList.
And all the code must be executed in a separate thread, otherwise latch will hang up the main thread and will be ANR.

how to add data obtained in OnComplete to ArrayList

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