Not getting response Volley android

Question

This is my code, I'm using volley to call a web service

private void sendRequest(){

    StringRequest stringRequest = new StringRequest(JSON_URL,
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    showJSON(response);


                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    Toast.makeText(MainActivity.this,error.getMessage(),Toast.LENGTH_LONG).show();
                }
            });

    RequestQueue requestQueue = Volley.newRequestQueue(this);
    requestQueue.add(stringRequest);
}

Anything wrong, getting NullPointerException

URL:

https://www.bgr.ionidea.com/math_lms/webservice/rest/server.php?wstoken=840e7d1cb52ca12239b01926310e0c68&wsfunction=local_math_get_android_version&moodlewsrestformat=json

ShowJson method

 private void showJSON(String json){
        ParseJSON pj = new ParseJSON(json);
        pj.parseJSON();
        CustomList cl = new CustomList(this, ParseJSON.id,ParseJSON.app_version);
        listView.setAdapter(cl);
    }

Parse JSON class

public class ParseJSON {

    public static String[] id;
    public static String[] app_version;


    public static final String JSON_ARRAY = "result";
    public static final String KEY_ID = "id";
    public static final String KEY_APP_VERSION = "app_version";


    private JSONArray users = null;

    private String json;

    public ParseJSON(String json){
        this.json = json;
    }

    protected void parseJSON(){
        JSONObject jsonObject=null;
        try {
            jsonObject = new JSONObject(json);
            users = jsonObject.getJSONArray(JSON_ARRAY);

            id = new String[users.length()];
            app_version = new String[users.length()];


            for(int i=0;i<users.length();i++){
                JSONObject jo = users.getJSONObject(i);
                id[i] = jo.getString(KEY_ID);
                app_version[i] = jo.getString(KEY_APP_VERSION);

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

Answer 1

Solution :

I found the Solution your id field you are taking in class is String and in response you will get the Integer value. That's why the error is occure.

Explantion :

In your response you get this "id":1 but actually you require this "id":"1".

Changing :

1.) change this public static String[] id; to public static Integer[] id;

2.) change this id[i] = jo.getString(KEY_ID); to id[i] = jo.getInt(KEY_ID);.

Answer 2

I think it has to do something with your JSON. You first ask for a JSONObject. In this JSONObject you ask for a JSONArray named result. In this JSONArray you ask for 2 values: id and app_version. So I think you JSON needs to look something like this:

{
    "result": [
      {"id": "1", "app_version": "1"}
    ]
}

With some more users it would look something like:

{
  "result": [
      {"id": "1", "app_version": "1"},
      {"id": "2", "app_version": "1"},
      {"id": "3", "app_version": "2"}
    ]
}

OR

If you can't change the JSON you need to make some changes:

1. Don't use a JSONObject at the start but start immediatly with the JSONArray like users = new JSONArray(json);
2. Like @Ironman told you need to change your id to be an int[] instead of a String[] and use getInt() instead of getString().

Answer 3

Your response is here:

[
  {
    "id": 1,
    "app_version": "1"
  }
]

Here , it is a list of json object. Object contains "id" that is integer and "app_version" is String. You can easily parse this response using Gson library. Here is sample code:

add this dependency in build.gradle file

compile 'com.google.code.gson:gson:2.2.4'

Now create a class like this:

import com.google.gson.annotations.SerializedName;
public class ResponseObject {

    @SerializedName("id")
    public Integer id;
    @SerializedName("app_version")
    public String app_version;

}

Now, you can parse your response using this way:

Type listType = new TypeToken<ArrayList<ResponseObject>>() {
                    }.getType();
 List<ResponseObject> yourClassList = new Gson().fromJson(jsonArray, listType);

Here, jsonArray is your response array.

Hope this will help you.