ListView does not update after JSON download

Question

I am trying to create a simple android app, where I get data from JSON and add it custom rows in a ListView.

I do get the data from the JSON but none of the rows are showing. I figured out that is because the rows are "created" before the JSON has finished downloading. How do I make the ListView update after the JSON has downloaded?

public class MainActivity extends AppCompatActivity {

    private RequestQueue mQueue;
    private static final String TAG = "MainActivity";
    String isDoneLoading = "false";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Log.d(TAG, "LOG STARTED");
        mQueue = Volley.newRequestQueue(this);

        ListView listView = (ListView) findViewById(R.id.listView);
        ArrayList<News> newsList = new ArrayList<>();

        // Create news objects

        jsonParse(newsList);

        NewsListAdapter adapter = new NewsListAdapter(this, R.layout.row, newsList);

        listView.setAdapter(adapter);

        Log.d(TAG, "RELOADING LISTVIEW");

    }


    private void jsonParse(final ArrayList<News> newsArray) {

        String url = "https://api.myjson.com/bins/kp9wz";

        JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        try {
                            JSONArray jsonArray = response.getJSONArray("employees");

                            for (int i = 0; i < jsonArray.length(); i++) {
                                JSONObject news_feed = jsonArray.getJSONObject(i);

                                String headline = news_feed.getString("firstname");
                                String category = news_feed.getString("mail");

                                Log.i(TAG, headline);

                                News newsData = new News(headline, category);

                                newsArray.add(newsData);
                            }

                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                error.printStackTrace();
            }
        });

        mQueue.add(request);
    }
}

Move your adapter code in _onResponse_ method after you parsed your data. — Piyush, Aug 23 '19 at 11:27
Please refer to https://stackoverflow.com/questions/18395753/how-to-dynamically-update-a-listview-with-custom-adapter — Sangeet Suresh, Aug 23 '19 at 11:29
@Piyush I get errors when doing that, because of the listView for some reason? — M. Holm, Aug 23 '19 at 11:31

score 2 · Accepted Answer · answered Aug 23 '19 at 11:33

Try with this changes

private RequestQueue mQueue;
private static final String TAG = "MainActivity";
String isDoneLoading = "false";
private NewsListAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Log.d(TAG, "LOG STARTED");
    mQueue = Volley.newRequestQueue(this);

    ListView listView = (ListView) findViewById(R.id.listView);
    ArrayList<News> newsList = new ArrayList<>();


    // Create news objects


    jsonParse(newsList);



     adapter = new NewsListAdapter(this, R.layout.row, newsList);

    listView.setAdapter(adapter);

    Log.d(TAG, "RELOADING LISTVIEW");


}


private void jsonParse(final ArrayList<News> newsArray) {

    String url = "https://api.myjson.com/bins/kp9wz";

    JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    try {
                        JSONArray jsonArray = response.getJSONArray("employees");


                        for (int i = 0; i < jsonArray.length(); i++) {
                            JSONObject news_feed = jsonArray.getJSONObject(i);

                            String headline = news_feed.getString("firstname");
                            String category = news_feed.getString("mail");

                            Log.i(TAG, headline);

                            News newsData = new News(headline, category);

                            newsArray.add(newsData);
                        }

                        updateList();

                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            error.printStackTrace();
        }
    });

    mQueue.add(request);

}

private void updateList(){
    if(adapter != null){
        adapter.notifyDataSetChanged();
    }
}

this is more helpful https://stackoverflow.com/questions/15422120/notifydatasetchange-not-working-from-custom-adapter — Code Kadiya, Aug 23 '19 at 11:35

score 0 · Answer 2 · answered Aug 23 '19 at 11:44

Currently you are not updating the Adapter after adding the new elements. Pass the adapter variable to the jsonParse method too. The content of the listview changes only when the adapter is notified of those changes in the arraylist used in the adapter. I your onCreate method

NewsListAdapter adapter = new NewsListAdapter(this, R.layout.row, newsList);
listView.setAdapter(adapter);
jsonParse(adapter, newsList);

Then in your onResponse method inside jsonParse method

try {
    JSONArray jsonArray = response.getJSONArray("employees");
    for (int i = 0; i < jsonArray.length(); i++) {
        JSONObject news_feed = jsonArray.getJSONObject(i);
        String headline = news_feed.getString("firstname");
        String category = news_feed.getString("mail");
        Log.i(TAG, headline);
        News newsData = new News(headline, category);

        newsArray.add(newsData);
        }
        // Notify the adapter after the for loop
        adapter.notifyDataSetChanged()

    } catch (JSONException e) {
        e.printStackTrace();
    }

ListView does not update after JSON download

2 Answers2