Calculating Score For Quiz App

[ensar topbas]

I do make a quiz app for Android. I parse JSON datas and have them written to radio group with radiobuttons. I could not exactly calculate the score. I tried to write a isRightAnswer method but even so, when i call the method the app crashes. trueResult is my score variable. The matter is mostly about the last part of the don't waste time with parsing part upside.

I wonder if this expression is wrong?

if(((RadioButton)grp_options.getChildAt(grp_options.getCheckedRadioButtonId())).getText().equals(rightAnswers.get(i)))

Or this?

 if(grp_options.getChildAt(checkedButtonId).toString().equals(rightAnswers.get(k))) 

Here is my QuizActiviyAdjectives class.

public class QuizActivityAdjectives extends Activity {

	public int trueResult = 0;
	public int i = 1;
	Button btn_nextQuestion;
	RadioGroup grp_options;
	TextView txt_questionAdjective;
	TextView txt_optionA;
	TextView txt_optionB;
	TextView txt_optionC;
	TextView txt_optionD;
	//int checkedButtonId = grp_options.getCheckedRadioButtonId();


	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_quiz_adjectives);
		// Hangi xml dosyasının dikkate alınacağı belirlendi.

		final List<String> questions = new ArrayList();
		final List<String> optionAs = new ArrayList();
		final List<String> optionBs = new ArrayList();
		final List<String> optionCs = new ArrayList();
		final List<String> optionDs = new ArrayList();
		final List<String> rightAnswers = new ArrayList();
		
		// Reading json file from assets folder
		StringBuffer sb = new StringBuffer();
		BufferedReader br = null;
		try {
			br = new BufferedReader(new InputStreamReader(getAssets().open(
					"Questions.json")));
			String temp;
			while ((temp = br.readLine()) != null)
				sb.append(temp);
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				br.close(); // stop reading
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		String myjsonstring = sb.toString();
		// Try to parse JSON
		try {
			// Creating JSONObject from String
			JSONObject jsonObjMain = new JSONObject(myjsonstring);

			// Creating JSONArray from JSONObject
			JSONArray jsonArray = jsonObjMain.getJSONArray("questions");

			// JSONArray has x JSONObject
			for (int i = 0; i < jsonArray.length(); i++) {

				// Creating JSONObject from JSONArray
				JSONObject jsonObj = jsonArray.getJSONObject(i);

				// Getting data from individual JSONObject
				int id = jsonObj.getInt("id");
				String question = jsonObj.getString("question");
				String optionA = jsonObj.getString("optionA");
				String optionB = jsonObj.getString("optionB");
				String optionC = jsonObj.getString("optionC");
				String optionD = jsonObj.getString("optionD");
				String rightAnswer = jsonObj.getString("rightAnswer");

				questions.add(jsonObj.getString("question"));
				optionAs.add(jsonObj.getString("optionA"));
				optionBs.add(jsonObj.getString("optionB"));
				optionCs.add(jsonObj.getString("optionC"));
				optionDs.add(jsonObj.getString("optionD"));
				rightAnswers.add(jsonObj.getString("rightAnswer"));

			}

		} catch (JSONException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		// The question is being prompted.
		txt_questionAdjective = (TextView) findViewById(R.id.txt_questionAdjective);
		txt_questionAdjective.setText(questions.get(0));
		grp_options = (RadioGroup) findViewById(R.id.grp_options);
		// Options are being prompted near the radioButtons.
		((RadioButton) grp_options.getChildAt(0)).setText(optionAs.get(0));
		((RadioButton) grp_options.getChildAt(1)).setText(optionBs.get(0));
		((RadioButton) grp_options.getChildAt(2)).setText(optionCs.get(0));
		((RadioButton) grp_options.getChildAt(3)).setText(optionDs.get(0));

		btn_nextQuestion = (Button) findViewById(R.id.btn_nextQuestion);
		// isRightAnswer(rightAnswers);
		btn_nextQuestion.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				promptTexts(optionAs, optionBs, optionCs, optionDs, questions, rightAnswers);

				if (i == 10) {
					
					Intent intent = new Intent(QuizActivityAdjectives.this, ResultActivity.class);
					// intent.putExtra("trueResult", trueResult);
					startActivity(intent);
				}
			}
		});		
	}

	public void promptTexts(List<String> optionAs, List<String> optionBs,
			List<String> optionCs, List<String> optionDs, List<String> questions,List<String> rightAnswers) {

		grp_options.clearCheck();
		txt_questionAdjective.setText(questions.get(i));
		((RadioButton) grp_options.getChildAt(0)).setText(optionAs.get(i));
		((RadioButton) grp_options.getChildAt(1)).setText(optionBs.get(i));
		((RadioButton) grp_options.getChildAt(2)).setText(optionCs.get(i));
		((RadioButton) grp_options.getChildAt(3)).setText(optionDs.get(i));
		i++;
//		if(((RadioButton) grp_options.getChildAt(grp_options.getCheckedRadioButtonId())).getText().equals(rightAnswers.get(i)))
//        {
//            trueResult++;
//        }
	}

	
/*	public void isRightAnswer(List<String> rightAnswers){
	    for(int k = 1 ; k< 10; k++) {
	        int checkedButtonId = grp_options.getCheckedRadioButtonId();
	        if(grp_options.getChildAt(checkedButtonId).toString().equals(rightAnswers.get(k)))
	        {
	            trueResult++;
	        }
	    }
	}
*/ 

If someone can write me the snippet or tips for the solution would be awesome. Thanks in advance.

[ensar topbas]

The problem is at this part.

if(((RadioButton) grp_options.getChildAt(grp_options.getCheckedRadioButtonId())).getText().equals(rightAnswers.get(i)))

Here is the log.

05-05 16:10:42.380: E/AndroidRuntime(16461): FATAL EXCEPTION: main
05-05 16:10:42.380: E/AndroidRuntime(16461): Process: org.example.ydsquizapp, PID: 16461
05-05 16:10:42.380: E/AndroidRuntime(16461): java.lang.NullPointerException
05-05 16:10:42.380: E/AndroidRuntime(16461): at org.example.ydsquizapp.QuizActivityAdjectives$1.onClick(QuizActivityAdjectives.java:124)
05-05 16:10:42.380: E/AndroidRuntime(16461): at android.view.View.performClick(View.java:4461)
05-05 16:10:42.380: E/AndroidRuntime(16461): at android.view.View$PerformClick.run(View.java:18523)
05-05 16:10:42.380: E/AndroidRuntime(16461): at android.os.Handler.handleCallback(Handler.java:733)
05-05 16:10:42.380: E/AndroidRuntime(16461): at android.os.Handler.dispatchMessage(Handler.java:95)
05-05 16:10:42.380: E/AndroidRuntime(16461): at android.os.Looper.loop(Looper.java:136)
05-05 16:10:42.380: E/AndroidRuntime(16461): at android.app.ActivityThread.main(ActivityThread.java:5118)
05-05 16:10:42.380: E/AndroidRuntime(16461): at java.lang.reflect.Method.invokeNative(Native Method)
05-05 16:10:42.380: E/AndroidRuntime(16461): at java.lang.reflect.Method.invoke(Method.java:515)
05-05 16:10:42.380: E/AndroidRuntime(16461): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
05-05 16:10:42.380: E/AndroidRuntime(16461): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:606)
05-05 16:10:42.380: E/AndroidRuntime(16461): at dalvik.system.NativeStart.main(Native Method)

How can i fix it ? Another way to write it?

[ensar topbas]

One more edit...

The problem at this part of the block below.

grp_options.getCheckedRadioButtonId()

if(((RadioButton) grp_options.getChildAt(3)).getText().equals(rightAnswers.get(i))) // Error at this expression
        {
            trueResult++;
        }

Is there another way to write it? Sorry for flooding.