ArrayList being empty after adding elements

Question

I have this android code which bring a JSON from a server and fill an ArrayList from that JSON I checked the size of the ArrayList "meals" inside the onresponse void it gives me 1 but when i check it after the StringRequest object i get 0 items . meals is defined in global scope and initialized inside the oncreateview function The Code:

               public View onCreateView(LayoutInflater inflater, ViewGroup container,  Bundle savedInstanceState) {
// Inflate the layout for this fragment
Log.i("debug","on create view");
View view =inflater.inflate(R.layout.fragment_meal_list,container,false);
ListView List ;
meals=new ArrayList<meal>();
String url="http://syriankitchen.tk/get_recent.php";
StringRequest mealsrequest = new StringRequest(Request.Method.GET, url, new Response.Listener<String>() {

    @Override
    public void onResponse(String response) {
        try{
            JSONObject object= new JSONObject(response);
            JSONArray mealsArray = object.getJSONArray("result");
            for(int i=0;i<mealsArray.length();i++){
                JSONObject cur = mealsArray.getJSONObject(i);
                int id= cur.getInt("id");
                String name= cur.getString("name");
                String description = cur.getString("description");
                int price = cur.getInt("price");
                meals.add(new meal(id,name,price,description));
            }
            Log.i("debug","meals size = "+meals.size());
        }
        catch(JSONException e){
            e.printStackTrace();
        }
    }
},new Response.ErrorListener(){
    @Override
    public void onErrorResponse(VolleyError error) {
        Toast.makeText(getActivity(),error.getMessage(),Toast.LENGTH_SHORT).show();
    }
});
Volley.newRequestQueue(getActivity()).add(mealsrequest);
ArrayList<String> strs=new ArrayList<String>();
String mealsnames[]=new String[meals.size()];
for(int i=0;i<meals.size();i++)strs.add(meals.get(i).getName());
strs.toArray(mealsnames);
Log.i("debug","meals ou size "+meals.size());
CustomList  adapter = new CustomList(getActivity(),mealsnames,meals);
List = (ListView)view.findViewById(R.id.list);
List.setAdapter(adapter);

you are confused as to what after means. callbacks are asynchronous. — njzk2
– njzk2, Commented Apr 21, 2016 at 18:26

Rohit Arya · Accepted Answer · 2016-04-21 18:34:03Z

The problem here is about understanding how asynchronous tasks work. When you are adding a volley request to the queque, it will run in background thread (off the main thread) and control will pass to the next line.

So, after this:

Volley.newRequestQueue(getActivity()).add(mealsrequest);

control passes to this:

ArrayList<String> strs=new ArrayList<String>();
String mealsnames[]=new String[meals.size()];

Now since meals is updated on the background thread, you are not able to get the data by the time control reaches String mealsnames[]=new String[meals.size()];

So you will get zero size (meals.size()) here.

Try to move this portion of the code into onResponse.

Try like this:

public void updateData(){
   ArrayList<String> strs=new ArrayList<String>();
   String mealsnames[]=new String[meals.size()];
   for(int i=0;i<meals.size();i++)strs.add(meals.get(i).getName());
   strs.toArray(mealsnames);
   Log.i("debug","meals ou size "+meals.size());
   CustomList  adapter = new CustomList(getActivity(),mealsnames,meals);
   List = (ListView)view.findViewById(R.id.list);
   List.setAdapter(adapter);
}

and call this method from onResponse:

@Override
public void onResponse(String response) {
    try{
        JSONObject object= new JSONObject(response);
        JSONArray mealsArray = object.getJSONArray("result");
        for(int i=0;i<mealsArray.length();i++){
            JSONObject cur = mealsArray.getJSONObject(i);
            int id= cur.getInt("id");
            String name= cur.getString("name");
            String description = cur.getString("description");
            int price = cur.getInt("price");
            meals.add(new meal(id,name,price,description));
        }
        Log.i("debug","meals size = "+meals.size());
        updateData();
    }
    catch(JSONException e){
        e.printStackTrace();
    }
}

Shadab Ansari · Accepted Answer · 2016-04-21 18:28:44Z

2

When you write this -

Volley.newRequestQueue(getActivity()).add(mealsrequest);

That means you are making an asynchronous call and that mealsrequest will run on another thread. You are printing -

Log.i("debug","meals ou size "+meals.size());

just after you make your mealsrequest. When control reaches this statement your network request is not completed yet. So apparently, you don't have anything in your list. Your list will be populated in onResponse() only, since that method is executed after the network request gets completed.

answered Apr 21, 2016 at 18:28

Shadab Ansari

7,0902 gold badges30 silver badges46 bronze badges

Collectives™ on Stack Overflow

ArrayList being empty after adding elements

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related