Converting Asnyctask to volley

Question

am new to android and am trying to convert the following asnyctask code to volley but getting a lot of errors advice on how to do it success fully

private class AsyncJsonObject extends AsyncTask<String, Void, String> {

        private ProgressDialog progressDialog;

        @Override
        protected String doInBackground(String... params) {

            HttpClient httpClient = new DefaultHttpClient(new BasicHttpParams());
            HttpPost httpPost = new HttpPost("http://192.168.0.2/testquiz/index.php");
            String jsonResult = "";

            try {
                HttpResponse response = httpClient.execute(httpPost);
                jsonResult = inputStreamToString(response.getEntity().getContent()).toString();
                System.out.println("Returned Json object " + jsonResult.toString());

            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return jsonResult;
        }
        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            progressDialog = ProgressDialog.show(QuizActivity.this, "Downloading Quiz","Wait....", true);
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            progressDialog.dismiss();
            System.out.println("Resulted Value: " + result);
            parsedObject = returnParsedJsonObject(result);
            if(parsedObject == null){
                return;
            }
            quizCount = parsedObject.size();
            firstQuestion = parsedObject.get(0);

            quizQuestion.setText(firstQuestion.getQuestion());
            String[] possibleAnswers = firstQuestion.getAnswers().split(",");
            optionOne.setText(possibleAnswers[0]);
            optionTwo.setText(possibleAnswers[1]);
            optionThree.setText(possibleAnswers[2]);
            optionFour.setText(possibleAnswers[3]);
        }

        private StringBuilder inputStreamToString(InputStream is) {
            String rLine = "";
            StringBuilder answer = new StringBuilder();
            BufferedReader br = new BufferedReader(new InputStreamReader(is));

            try {
                while ((rLine = br.readLine()) != null) {
                    answer.append(rLine);
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return answer;
        }
    }
    */
    private List<QuizWrapper> returnParsedJsonObject(String result) {

        List<QuizWrapper> jsonObject = new ArrayList<QuizWrapper>();
        JSONObject resultObject = null;
        JSONArray jsonArray = null;
        QuizWrapper newItemObject = null;
        try {
            resultObject = new JSONObject(result);
            System.out.println("Testing the water " + resultObject.toString());
            jsonArray = resultObject.optJSONArray("quiz_questions");
        }
        catch (JSONException e) {
            e.printStackTrace();
        }
        if (jsonArray != null) {     // check jsonArray is null?
            for (int i = 0; i < jsonArray.length(); i++) {
                JSONObject jsonChildNode = null;
                try {
                    jsonChildNode = jsonArray.getJSONObject(i);
                    int id = jsonChildNode.getInt("id");

                    String question = jsonChildNode.getString("question");
                    String answerOptions = jsonChildNode.getString("possible_answers");
                    int correctAnswer = jsonChildNode.getInt("correct_answer");
                    newItemObject = new QuizWrapper(id, question, answerOptions, correctAnswer);
                    jsonObject.add(newItemObject);
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        }
            return jsonObject;
        }

here is what i have achieved so far any help will be appreciated

public Object getQuestion() {
        JsonObjectRequest  jsonObjectRequest = new JsonObjectRequest(Request.Method.POST, showUrl, null, new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(JSONObject response) {
                try {
                    JSONArray questions = response.getJSONArray("questions");
                    for(int i=0; i<questions.length(); i++){
                        JSONObject quiz_questions = questions.getJSONObject(i);

                        String firstQuestion = quiz_questions.getString("firstQuestion");
                        String optionOne = quiz_questions.getString("optionOne");
                        String optionTwo = quiz_questions.getString("optionTwo");
                        String optionThree = quiz_questions.getString("optionThree");
                        String optionFour = quiz_questions.getString("optionFour");

                        quizQuestion.append(firstQuestion+ "" +optionOne+"" +optionTwo+""+optionThree+""+optionFour+ "");




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

            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {

            }
        });
        requestQueue.add(jsonObjectRequest);
        return question;
    }

the errors occuring

FATAL EXCEPTION: main

Process: test.com.okcupid, PID: 31544
                                                                      java.lang.RuntimeException: Unable to start activity ComponentInfo{test.com.okcupid/test.com.okcupid.QuizActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'com.android.volley.Request com.android.volley.RequestQueue.add(com.android.volley.Request)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)    
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'com.android.volley.Request com.android.volley.RequestQueue.add(com.android.volley.Request)' on a null object reference
at test.com.okcupid.QuizActivity.getQuestion(QuizActivity.java:175)
at test.com.okcupid.QuizActivity.onCreate(QuizActivity.java:118)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
at android.app.ActivityThread.-wrap12(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6119) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

@NickCardoso i have updated the question plus the error – Remy Mar 01 '17 at 21:32 — Remy, Mar 01 '17 at 21:32

score 0 · Answer 1 · answered Mar 01 '17 at 21:36

The problem is in this line:

requestQueue.add(jsonObjectRequest);

At the point it reaches the line requestQueue is null for some reason. You need to make sure the variable gets initialized before using it. If you're not able to be sure, then always wrap it with

if (requestQueue != null)

You need to take a quick tutorial on how multi threading works also. Because in getQuestion you kick off an asynchronous request (JsonObjectRequest), the lines after it (requestQueue.add(jsonObjectRequest) and the return statement) are going to be executed before onResponse

Converting Asnyctask to volley

1 Answers1