From Android JSON array to a list of items

Question

From Android JSON array to a list of items

In my android app, I have encountered an issue while trying to parse a JSONArray into an ArrayList. The PHP script returns the expected results correctly, but when attempting to add the results to the ArrayList in Java, a null pointer exception occurs 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);

    }

java android json arraylist arrays

Answer 1

Answer №1

Here is a suggestion that might assist you:

public void agencySearch(String searchTerm)    {
        // Defining the URL for searching by city
        String searchUrl = "http://www.infinitycodeservices.com/get_agency_by_city.php";
        // Creating parameters for the search
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("City", searchTerm));

        // Retrieving JSON data from the specified URL
        JSONArray jsonResult = jParser.getJSONFromUrl(searchUrl, params);

       ArrayList<HashMap<String, String>> resultsList = new  ArrayList<HashMap<String, String>>();

        for (int i = 0; i < jsonResult.length(); i++) {
            HashMap<String, String> map = new HashMap<String, String>();

            try {
                JSONObject obj = jsonResult.getJSONObject(position);
                //Populate the map
               Iterator<String> iter = obj.keys();
                while(iter.hasNext())   {
                    String currentKey = it.next();
                    map.put(currentKey, obj.getString(currentKey));
                }
                resultsList.add(map);

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

            }

        };

        MainActivity.setResultsList(resultsList);

    }

Answer 2

Here is a suggestion that might assist you:

public void agencySearch(String searchTerm)    {
        // Defining the URL for searching by city
        String searchUrl = "http://www.infinitycodeservices.com/get_agency_by_city.php";
        // Creating parameters for the search
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("City", searchTerm));

        // Retrieving JSON data from the specified URL
        JSONArray jsonResult = jParser.getJSONFromUrl(searchUrl, params);

       ArrayList<HashMap<String, String>> resultsList = new  ArrayList<HashMap<String, String>>();

        for (int i = 0; i < jsonResult.length(); i++) {
            HashMap<String, String> map = new HashMap<String, String>();

            try {
                JSONObject obj = jsonResult.getJSONObject(position);
                //Populate the map
               Iterator<String> iter = obj.keys();
                while(iter.hasNext())   {
                    String currentKey = it.next();
                    map.put(currentKey, obj.getString(currentKey));
                }
                resultsList.add(map);

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

            }

        };

        MainActivity.setResultsList(resultsList);

    }

Answer 3

Answer №2

It is recommended to utilize a custom method that converts your JSONArray into a List instead of manually iterating and constructing the List.

Instructions on how to call this method :

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

Method to convert JSON array into List :

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

Method to convert JSON into Object :

private Object parseJson(Object json) throws JSONException {
    if (json == JSONObject.NULL) {
        return null;
    } else if (json instanceof JSONObject) {
        return mapFromJson((JSONObject) json);
    } else if (json instanceof JSONArray) {
        return convertToList((JSONArray) json);
    } else {
        return json;
    }
}

Method to convert JSON into Map :

public Map<String, String> mapFromJson(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, parseJson(object.get(key)).toString());
    }
    return map;
}

Answer 4

It is recommended to utilize a custom method that converts your JSONArray into a List instead of manually iterating and constructing the List.

Instructions on how to call this method :

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

Method to convert JSON array into List :

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

Method to convert JSON into Object :

private Object parseJson(Object json) throws JSONException {
    if (json == JSONObject.NULL) {
        return null;
    } else if (json instanceof JSONObject) {
        return mapFromJson((JSONObject) json);
    } else if (json instanceof JSONArray) {
        return convertToList((JSONArray) json);
    } else {
        return json;
    }
}

Method to convert JSON into Map :

public Map<String, String> mapFromJson(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, parseJson(object.get(key)).toString());
    }
    return map;
}

From Android JSON array to a list of items

Answer №1

Answer №2

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