Android JSONArray to ArrayList

Question

I am trying to parse a JSONArray into and ArrayList in my android app. The PHP script correctly retuns the expected results, however the Java fails with a null pointer exception at resultsList.add(map)

public void agencySearch(String tsearch) {
 // Setting the URL for the Search by Town
 String url_search_agency = "http://www.infinitycodeservices.com/get_agency_by_city.php";
 // Building parameters for the search
 List<NameValuePair> params = new ArrayList<NameValuePair>();
 params.add(new BasicNameValuePair("City", tsearch));
 // Getting JSON string from URL
 JSONArray json = jParser.getJSONFromUrl(url_search_agency, params);
 for (int i = 0; i < json.length(); i++) {
 HashMap<String, String> map = new HashMap<String, String>();
 try {
 JSONObject c = (JSONObject) json.get(i);
 //Fill map
 Iterator iter = c.keys();
 while(iter.hasNext()) {
 String currentKey = (String) iter.next();
 map.put(currentKey, c.getString(currentKey));
 }
 resultsList.add(map);
 }
 catch (JSONException e) {
 e.printStackTrace();
 }
 };
 MainActivity.setResultsList(resultsList);
 }

• Shayan Pourvatan: where you initialize resultsList in your code?
• Stack Exchange Broke The Law: That's because resultsList is null.
• Senthamil Thendral S: have you initialize resultList???
• Stack Exchange Broke The Law: possible duplicate of What is a Null Pointer Exception, and how do I fix it?

Answer 1

try like this may help you,

public void agencySearch(String tsearch) {
 // Setting the URL for the Search by Town
 String url_search_agency = "http://www.infinitycodeservices.com/get_agency_by_city.php";
 // Building parameters for the search
 List<NameValuePair> params = new ArrayList<NameValuePair>();
 params.add(new BasicNameValuePair("City", tsearch));
 // Getting JSON string from URL
 JSONArray json = jParser.getJSONFromUrl(url_search_agency, params);
 ArrayList<HashMap<String, String>> resultsList = new ArrayList<HashMap<String, String>>();
 for (int i = 0; i < json.length(); i++) {
 HashMap<String, String> map = new HashMap<String, String>();
 try {
 JSONObject c = json.getJSONObject(position);
 //Fill map
 Iterator<String> iter = c.keys();
 while(iter.hasNext()) {
 String currentKey = it.next();
 map.put(currentKey, c.getString(currentKey));
 }
 resultsList.add(map);
 }
 catch (JSONException e) {
 e.printStackTrace();
 }
 };
 MainActivity.setResultsList(resultsList);
 }

• IrishCarBomb: Nice catch. My declaration for resultsList was elsewhere in the class code. This was my original definition ArrayList<Map<String, String>> resultsList; after adding the = new ArrayList<Map<String, String>>() to the end of that line the exception was gone. Thanks again. Maybe I should have gotten some sleep and checked it again before asking the question. Simple syntax error. Hopefully it will help someone else as well.

Answer 2

Use custom method which convert your JSONArray to List instead of iterate and build List.

How to call :

try {
 ArrayList<HashMap<String,String>> list = (ArrayList<HashMap<String,String>>) toList(json);
} catch (JSONException e) {
 e.printStackTrace();
}

Convert json array to List :

private List toList(JSONArray array) throws JSONException {
 List list = new ArrayList();
 int size = array.length();
 for (int i = 0; i < size; i++) {
 list.add(fromJson(array.get(i)));
 }
 return list;
}

Convert json to Object :

private Object fromJson(Object json) throws JSONException {
 if (json == JSONObject.NULL) {
 return null;
 } else if (json instanceof JSONObject) {
 return jsonToMap((JSONObject) json);
 } else if (json instanceof JSONArray) {
 return toList((JSONArray) json);
 } else {
 return json;
 }
}

Convert json to map :

public Map<String, String> jsonToMap(JSONObject object) throws JSONException {
 Map<String, String> map = new HashMap();
 Iterator keys = object.keys();
 while (keys.hasNext()) {
 String key = (String) keys.next();
 map.put(key, fromJson(object.get(key)).toString());
 }
 return map;
}

• Hareshkumar Chhelana: Have you try this @IrishCarBomb ?
• IrishCarBomb: I didn't. Is this using the GSON LIB?