Cannot get a random row from database to display as Q&A on main activity

Question

Is this method correct?

public List<Question> getQuestionSet(int i){
        List<Question> questionSet = new ArrayList<Question>();
       Cursor c = db.rawQuery("SELECT * FROM quiztable ORDER BY RANDOM() LIMIT X" + i, null);
        while (c.moveToNext()){
            Question q = new Question();
            q.setQuestion(c.getString(1));
            q.setAnswer(c.getString(2));
            q.setOption1(c.getString(3));
            q.setOption2(c.getString(4));
            questionSet.add(q);
        }
        return questionSet;

If yes, how do i create a method of displaying each question from my database individually in random order.. sorry. i have no idea what to do...

EDIT: I tried changing the code above to your code. Now another question. This is the code i have in my MainActivity file:

public class Second extends Activity {

TextView questionTextView;
DBAdapter db = new DBAdapter(this);
Cursor mCursor;



@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.second);

    TextView questionTextView = (TextView) findViewById(R.id.question);
    RadioGroup radioGroup = (RadioGroup) findViewById(R.id.radioGroup1);
    RadioButton rb0 = (RadioButton) findViewById(R.id.radio0);
    RadioButton rb1 = (RadioButton) findViewById(R.id.radio1);
    RadioButton rb2 = (RadioButton) findViewById(R.id.radio2);

    db.open();
    db.getQuestionSet(1);
    String question = mCursor.getString(mCursor.getColumnIndex(DBAdapter.KEY_QUESTIONS));
    String answer = mCursor.getString(mCursor.getColumnIndex(DBAdapter.KEY_ANSWERS));
    String opt1 = mCursor.getString(mCursor.getColumnIndex(DBAdapter.KEY_CHOICE1));
    String opt2 = mCursor.getString(mCursor.getColumnIndex(DBAdapter.KEY_CHOICE2));
    questionTextView.setText(question);
    rb0.setText(answer);
    rb1.setText(opt1);
    rb2.setText(opt2);

}

}

I get an error when i try to run it. i know my code is incorrect. but i am not sure how to correct it. To be more specific, what i am trying to do is create an app quiz. I managed to create a database. I could insert/update/delete questions and answers thru the application. But i can't display the questions stored in my database so i could answer the questions and grade it. thank you for your help guys. Im a beginner. been studying eclipse for a month now.. and i cant even create a simple quiz app. :(

Thank you. Here is the error shown in Logcat:

 09-03 15:29:49.516: D/AndroidRuntime(4091): Shutting down VM
 09-03 15:29:49.516: W/dalvikvm(4091): threadid=1: thread exiting with uncaught exception (group=0x40015560)
 09-03 15:29:49.527: E/AndroidRuntime(4091): FATAL EXCEPTION: main
 09-03 15:29:49.527: E/AndroidRuntime(4091): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dtan.quiz/com.dtan.quiz.Second}: java.lang.NullPointerException
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at android.os.Handler.dispatchMessage(Handler.java:99)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at android.os.Looper.loop(Looper.java:123)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at android.app.ActivityThread.main(ActivityThread.java:3683)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at java.lang.reflect.Method.invokeNative(Native Method)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at   java.lang.reflect.Method.invoke(Method.java:507)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at dalvik.system.NativeStart.main(Native Method)
 09-03 15:29:49.527: E/AndroidRuntime(4091): Caused by: java.lang.NullPointerException
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at com.dtan.quiz.Second.onCreate(Second.java:30)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
 09-03 15:29:49.527: E/AndroidRuntime(4091):    ... 11 more

biegleux · Accepted Answer · 2012-09-03 07:29:30Z

1

public List<Question> getQuestionSet(int i) {
    List<Question> questionSet = new ArrayList<Question>();
    final Cursor c = db.rawQuery("SELECT * FROM quiztable ORDER BY RANDOM() LIMIT " + i, null);
    if (c != null) {
        try {
            while (c.moveToNext()) {
                Question q = new Question();
                q.setQuestion(c.getString(1));
                q.setAnswer(c.getString(2));
                q.setOption1(c.getString(3));
                q.setOption2(c.getString(4));
                questionSet.add(q);
            }
        } finally {
            c.close();
        }
    }
    return questionSet;
}

EDIT:

You have not initialized your Cursor. But it's useless as you are returning List from your getQuestionSet() method, use it instead.

List<Question> questions = db.getQuestionSet(1);
if (questions != null && !questions.isEmpty()) {
   Question question = questions.get(0);
   now use:
   question.getQuestion();
   question.getAnswer();
   question.getOption1();
   question.getOption2();
}

edited Sep 3, 2012 at 7:29

answered Sep 3, 2012 at 7:01

biegleux

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4 Comments

omi0301 Over a year ago

Thank you for your answer. I managed to change my code. However, on my main activity I used this:

omi0301 Over a year ago

Thank you for your answer. please see edit above if you have time. Thanks.. :)

omi0301 Over a year ago

I tried changing the code. But it does not show the value of the entries in my database, it just shows "textview", and "radiobutton" for the 3 radiobuttons. I appreciate your time.

biegleux Over a year ago

Try to debug your code to find out what is wrong, if you have some fields in your db, if method returned some results etc.

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