protected Void doInBackground(Void... arg0) {
            databasehandler sh = new databasehandler();

            // Making a request to url and getting response
            String jsonStr = sh.makeServiceCall(url);

            Log.e(TAG, "Response from url: " + jsonStr);

            if (jsonStr != null) {
                try {
                    JSONArray jsonArray = new JSONArray(jsonStr);


                    // looping through currencies
                    for (int i = 0; i < jsonArray.length(); i++) {
                        JSONObject c = jsonArray.getJSONObject(i);

                        String name = c.getString("name");
                        String symbol = c.getString("symbol");
                        Double price_usd = c.getDouble("price_usd");
                        Double price_eur = c.getDouble("price_eur");
                        Double price_btc = c.getDouble("price_btc");
                        Double volume_eur = c.getDouble("volume_eur");
                        Double market_cap_usd = c.getDouble("market_cap_usd");
                        Double percent_change_1h = c.getDouble("percent_change_1h");
                        Double percent_change_24h = c.getDouble("percent_change_24h");
                        Double percent_change_7d = c.getDouble("percent_change_7d");


                        // tmp hash map for single contact
                        HashMap<String, String> currency = new HashMap<>();

                        // adding each child node to HashMap key => value

                        currency.put("name", name);
                        currency.put("symbol", symbol);

                        // adding currency to currencyList
                        currencyList.add(currency);
                    }
                } catch (final JSONException e) {
                    Log.e(TAG, "Json parsing error: " + e.getMessage());
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            Toast.makeText(getApplicationContext(),
                                    "Json parsing error: " + e.getMessage(),
                                    Toast.LENGTH_LONG)
                                    .show();
                        }
                    });

                }
            } else {
                Log.e(TAG, "Couldn't get json from server.");
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getApplicationContext(),
                                "Couldn't get json from server. Check LogCat for possible errors!",
                                Toast.LENGTH_LONG)
                                .show();
                    }
                });

            }

            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            // Dismiss the progress dialog
            if (pDialog.isShowing())
                pDialog.dismiss();
            /**
             * Updating parsed JSON data into ListView
             * */
            ListAdapter adapter = new SimpleAdapter(
                    currencyTableView.this, currencyList,
                    R.layout.list_crypto_items, new String[]{"name", "symbol"}, new int[]{R.id.name,
                    R.id.symbol});

            lv.setAdapter(adapter);
        }

    }