Unable to populate ListView from ArrayList

Question

ChooseCategory.java

        public class ChooseCategory extends ListActivity {
            private ListView lv;
            //ArrayAdapter<FoodStores> arrayAdapter;
            private ArrayList<FoodStores> storefoodList;
        private String URL_STORES = "http://10.0.2.2/get_stores.php";
         @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                 lv = (ListView)findViewById(R.id.list);
                 storefoodList = new ArrayList<FoodStores>();
                 new GetFoodStores().execute();

        }

    private class GetFoodStores extends AsyncTask<Void,Void,Void> {
            @Override
            protected void onPreExecute(){
                super.onPreExecute();
            }

            @Override
            protected Void doInBackground(Void... arg0) {
                ServiceHandlerFood jsonParserFood = new ServiceHandlerFood();
                String json = jsonParserFood.makeServiceCall(URL_STORES, ServiceHandlerFood.GET);
                Log.e("Response: ", " > " + json);
                if(json != null){
                    try{
                        JSONObject jsonObj = new JSONObject(json);
                        if(jsonObj != null){
                            JSONArray storeListFood = jsonObj.getJSONArray("storelistfood");
                            for(int i = 0; i < storeListFood.length(); i++){
                                JSONObject storeFoodObj = (JSONObject) storeListFood.get(i);
                                FoodStores foodStores = new FoodStores(storeFoodObj.getInt("id"),storeFoodObj.getString("STORENAME"));
                                storefoodList.add(foodStores);

                            }
                        }
                    }catch(JSONException e){
                        e.printStackTrace();
                    }
                }else{
                    Log.e("JSON Data", "No data received from server");
                }
                return null;
            }
@Override
        protected void onPostExecute(Void result){
            super.onPostExecute(result);
            populateListView();
        }
    }

Here is the function of my populateListView

private void populateListView(){
        List<String> labels = new ArrayList<String>();
        for(int i = 0; i < storefoodList.size(); i++){
            labels.add(storefoodList.get(i).getName());
        }
        ArrayAdapter<String> listAdapter = new ArrayAdapter<String>(this,R.layout.restaurant_list,labels);
        Log.d("Labels:", labels.toString());         
        lv.setAdapter(listAdapter);    
    }

What I am trying to do here is to get the list of stores from PHP to Android via JSON and store them in ArrayList and then populate them into ListView. I have tried displaying labels, it is displaying the correct stuff.

The error from Emulator is that it just shows blank screen and then it crashes. The error from logcat is

java.lang.NullPointerException
            at call.rocket.user.callarocket.ChooseCategory.populateListView

Answer 1

Do like

ArrayAdapter<String> listAdapter = new ArrayAdapter<String>(this,R.layout.restaurant_list,labels);
setListAdapter(listAdapter);

as you directly extends ListActivity also remove

 lv = (ListView)findViewById(R.id.list);

and make sure your ListView id is android:id="@android:id/list"

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