Android error while adding data to ArrayList

Question

I send POST request and get JSON object. I have parsed it, but when I'm trying to add it to the ArrayList for RecyclerView, I get 0 size of ArrayList. My AsyncTask:

new AsyncTask<Void, Void, Void>() {
            ProgressDialog loading;

            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                loading = ProgressDialog.show(LectorsListActivity.this, null, "Please Wait", true, false);
            }

            @Override
            protected Void doInBackground(Void... params) {
                try {
                    LoginLectorUtils httpUtils = new LoginLectorUtils();
                    String name, uniqueId, photoUrl;
                    JSONArray array = new JSONArray(httpUtils.sendPostRequest(REQUEST_URL));

                    for (int i = 0; i < array.length(); i++) {
                        JSONObject jsonObject = array.getJSONObject(i);

                        name = jsonObject.getString("name");
                        uniqueId = jsonObject.getString("unique_id");
                        photoUrl = jsonObject.getString("photo_url");

                        //if (!name.equals("") && !uniqueId.equals("") && !photoUrl.equals("")) {
                            data.add(new LectorsDataModel(name, uniqueId, photoUrl)); // Here i'm adding new items
                        //}
                    }

                } catch (Exception e) {
                    Log.e("LectorsListActivity", "Can't create JSONArray");
                }

                return null;
            }

            @Override
            protected void onPostExecute(final Void str) {
                super.onPostExecute(str);
                loading.dismiss();
            }
        }.execute();

        //data = new ArrayList<LectorsDataModel>();
        //data.add(new LectorsDataModel("", "", ""));

        Toast.makeText(LectorsListActivity.this, Integer.toString(data.size()), Toast.LENGTH_SHORT).show(); // Shows 0

        adapter = new LectorsAdapter(data, this);
        recyclerView.setAdapter(adapter);

you need to get familiar with what async means in asynctask. — njzk2
– njzk2, Commented Feb 4, 2016 at 23:13

Rohit5k2 · Accepted Answer · 2016-02-03 19:47:02Z

1

You code is being executed before you get the result because you are finding the size before data is available.

You have two solutions here

Solution 1

Add

Toast.makeText(LectorsListActivity.this, Integer.toString(data.size()), Toast.LENGTH_SHORT).show(); // Shows 0
adapter = new LectorsAdapter(data, this);
recyclerView.setAdapter(adapter);

inside onPostExecute() method.

Solution 2

Add

adapter.notifyDataSetChanged();

inside onPostExecute() method.

And put

adapter = new LectorsAdapter(data, this);

before calling the AsyncTask

edited Feb 3, 2016 at 19:47

answered Feb 3, 2016 at 19:26

Rohit5k2

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2 Comments

Rohit5k2 Over a year ago

You can as I have mentioned in Solution 2, but you will have to tell the adapter that data is available and now you can refresh.

Roman Svyatnenko Over a year ago

@Rohit5k2, Solution 2 not working, I am getting NullPointer

lkz · Accepted Answer · 2016-02-04 23:03:45Z

You can also try use RxAndroid (+optional Retrolambda). Check below example which should target yout problem aswell.

Create observable which will emit your items:

    rx.Observable<List<Item>> fetchItems() {
    return Observable.create(
        subscriber -> {
            try {
                Thread.sleep(2000); //simulate long operation
                subscriber.onNext(yourItems());
            } catch (InterruptedException e) {
                subscriber.onError(e);
            }
        }
    );
}

and subscribe to it:

    Subscription subscription = fetchItems()
        .subscribeOn(Schedulers.newThread())
        .observeOn(AndroidSchedulers.mainThread())
        .doOnSubscribe(() -> mProgressDialog = ProgressDialog.show(getContext(), "Progress", "Please Wait", true))
        .doOnTerminate(this::dismissProgressDialog)
        .subscribe(
            items -> {
                recyclerView.setAdapter(new SimpleAdapter(items));
                dismissProgressDialog();
            },
            e -> Log.e("onError", e.getMessage())
        );

Code in 'Observable.create' will be executed in new thread, rest in Android UI thread.

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