Android SQLite Quiz App

Question

I am trying to create an app that lets you take a quiz, for example, a world history quiz. On the main activity, the user presses the enter button to choose the category of a quiz, let's say we choose world history, then it's supposed to go to the world history activity but it crashes. Here is my code so far, don't know what is wrong with it:

DatabaseHandler.java

public class DatabaseHandler extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "quiz";
    private static final String TABLE_NAME = "worldhistory";
    private static final String KEY_ID = "id";
    private static final String QUESTIONS = "question";
    private static final String ANSWER = "answer";
    private static final String OPTIONA = "optiona";
    private static final String OPTIONB = "optionb";
    private static final String OPTIONC = "optionc";
    private static final String OPTIOND = "optiond";

    private SQLiteDatabase dba;

    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_TABLE = "CREATE TABLE IF NOT EXISTS " + TABLE_NAME + " ( "
                + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + QUESTIONS + " TEXT, "
                + ANSWER + " TEXT, " + OPTIONA + " TEXT, " + OPTIONB + " TEXT, " + OPTIONC
                + " TEXT, " + OPTIOND + " TEXT)";

        db.execSQL(CREATE_TABLE);

        addQuestions();
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXITS " + TABLE_NAME);
        onCreate(db);
    }

    // creating the questions, options, and answers
    private void addQuestions() {
        Question q1 = new Question("World War I began in which year?", "1923",
                "1938", "1917", "1914", "D");
        this.addQuestion(q1);

        Question q2 = new Question("Adolf Hitler was born in which country?",
                "France", "Germany", "Austria", "Hungary", "C");
        this.addQuestion(q2);

        //add more questions
    }

    // addding new questions to db
    public void addQuestion(Question question) {
        ContentValues values = new ContentValues();
        values.put(QUESTIONS, question.getQuestion());
        values.put(ANSWER, question.getAnswer());
        values.put(OPTIONA, question.getOptionA());
        values.put(OPTIONB, question.getOptionB());
        values.put(OPTIONC, question.getOptionC());
        values.put(OPTIOND, question.getOptionD());

        dba.insert(TABLE_NAME, null, values);
    }

    public List<Question> getAllQuestions() {
        List<Question> questionList = new ArrayList<Question>();

        String query = "SELECT * FROM " + TABLE_NAME;
        dba = this.getReadableDatabase();
        Cursor cursor = dba.rawQuery(query, null);

        if (cursor.moveToFirst()) {
            do {
                Question quest = new Question();
                quest.setID(cursor.getInt(0));
                quest.setQuestion(cursor.getString(1));
                quest.setAnswer(cursor.getString(2));
                quest.setOptionA(cursor.getString(3));
                quest.setOptionB(cursor.getString(4));
                quest.setOptionC(cursor.getString(5));
                quest.setOptionD(cursor.getString(6));

                questionList.add(quest);

            } while (cursor.moveToNext());
        }

        cursor.close();
        dba.close();
        return questionList;
    }

    public int rowCount() {
        int row = 0;
        String query = "SELECT * FROM " + TABLE_NAME;
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query, null);
        row = cursor.getCount();

        cursor.close();
        return row;
    }
}

Question.java

public class Question {
    private int ID;
    private String Question, optionA, optionB, optionC, optionD, Answer;

    public Question() {
        ID = 0;
        Question = "";
        optionA = "";
        optionB = "";
        optionC = "";
        optionD = "";
        Answer = "";
    }

    public Question(String Question, String optionA, String optionB, String optionC,
                    String optionD, String Answer) {
        this.Question = Question;
        this.optionA = optionA;
        this.optionB = optionB;
        this.optionC = optionC;
        this.optionD = optionD;
        this.Answer = Answer;
    }

    public int getID() {
        return ID;
    }

    public String getQuestion() {
        return Question;
    }

    public String getOptionA() {
        return optionA;
    }

    public String getOptionB() {
        return optionB;
    }

    public String getOptionC() {
        return optionC;
    }

    public String getOptionD() {
        return optionD;
    }

    public String getAnswer() {
        return Answer;
    }

    public void setID(int ID) {
        this.ID = ID;
    }

    public void setQuestion(String Question) {
        this.Question = Question;
    }

    public void setOptionA(String optionA) {
        this.optionA = optionA;
    }

    public void setOptionB(String optionB) {
        this.optionB = optionB;
    }

    public void setOptionC(String optionC) {
        this.optionC = optionC;
    }

    public void setOptionD(String optionD) {
        this.optionD = optionD;
    }

    public void setAnswer(String answer) {
        Answer = answer;
    }
}

WorldHistory.java

public class WorldHistory extends AppCompatActivity {
    List<Question> questionList;
    int score = 0;
    int questionID = 0;

    Question currentQuestion;
    TextView txtQuestion;
    RadioButton rbtnA, rbtnB, rbtnC, rbtnD;
    Button btnNext;

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

        DatabaseHandler dba = new DatabaseHandler(this);
        questionList = dba.getAllQuestions();
        currentQuestion = questionList.get(questionID);

        txtQuestion = (TextView) findViewById(R.id.txtQuestion);
        rbtnA = (RadioButton) findViewById(R.id.rtbOptionA);
        rbtnB = (RadioButton) findViewById(R.id.rtbOptionB);
        rbtnC = (RadioButton) findViewById(R.id.rtbOptionC);
        rbtnD = (RadioButton) findViewById(R.id.rtbOptionD);
        btnNext = (Button) findViewById(R.id.btnNext);

        setQuestionView();
    }

    private void setQuestionView() {
        txtQuestion.setText(currentQuestion.getQuestion());
        rbtnA.setText(currentQuestion.getOptionA());
        rbtnB.setText(currentQuestion.getOptionB());
        rbtnC.setText(currentQuestion.getOptionC());
        rbtnD.setText(currentQuestion.getOptionD());
        questionID++;
    }
}

Here's the error message:

07-10 20:04:11.346 2514-2514/com.example.nasimahmed.quizgame E/AndroidRuntime: FATAL EXCEPTION: main
                                                                               Process: com.example.nasimahmed.quizgame, PID: 2514


java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nasimahmed.quizgame/com.example.nasimahmed.quizgame.WorldHistory}: java.lang.NullPointerException: Attempt to invoke virtual method 'long android.database.sqlite.SQLiteDatabase.insert(java.lang.String, java.lang.String, android.content.ContentValues)' on a null object reference


                                                                                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                                   at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                   at android.os.Looper.loop(Looper.java:148)
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                                   at java.lang.reflect.Method.invoke(Native Method)
                                                                                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                                Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long android.database.sqlite.SQLiteDatabase.insert(java.lang.String, java.lang.String, android.content.ContentValues)' on a null object reference
                                                                                   at com.example.nasimahmed.quizgame.DatabaseHandler.addQuestion(DatabaseHandler.java:81)
                                                                                   at com.example.nasimahmed.quizgame.DatabaseHandler.addQuestions(DatabaseHandler.java:61)
                                                                                   at com.example.nasimahmed.quizgame.DatabaseHandler.onCreate(DatabaseHandler.java:46)
                                                                                   at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:251)
                                                                                   at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:187)
                                                                                   at com.example.nasimahmed.quizgame.DatabaseHandler.getAllQuestions(DatabaseHandler.java:89)
                                                                                   at com.example.nasimahmed.quizgame.WorldHistory.onCreate(WorldHistory.java:29)
                                                                                   at android.app.Activity.performCreate(Activity.java:6237)
                                                                                   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                                   at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                   at android.os.Looper.loop(Looper.java:148) 
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:5417)

Post the stack trace and Implement the onClick Listener for the button — TechnoBlahble, Jul 11 '16 at 00:02
It's a pure `NullPointer`..!! How can this have 4 up-votes ?? @Nasim where is your code to open the `Sqlite` ?? something like `getReadable/WriteableDatabase` ?? — Janki Gadhiya, Jul 11 '16 at 04:57

score 2 · Accepted Answer · answered Jul 11 '16 at 01:01

Use this DatabaseHandler instead:

public class DatabaseHandler extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "quiz";
    private static final String TABLE_NAME = "worldhistory";
    private static final String KEY_ID = "id";
    private static final String QUESTIONS = "question";
    private static final String ANSWER = "answer";
    private static final String OPTIONA = "optiona";
    private static final String OPTIONB = "optionb";
    private static final String OPTIONC = "optionc";
    private static final String OPTIOND = "optiond";

    private SQLiteDatabase dba;

    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_TABLE = "CREATE TABLE IF NOT EXISTS " + TABLE_NAME + " ( "
                + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + QUESTIONS + " TEXT, "
                + ANSWER + " TEXT, " + OPTIONA + " TEXT, " + OPTIONB + " TEXT, " + OPTIONC
                + " TEXT, " + OPTIOND + " TEXT)";

        db.execSQL(CREATE_TABLE);

        addQuestions(db);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXITS " + TABLE_NAME);
        onCreate(db);
    }

    // creating the questions, options, and answers
    private void addQuestions(SQLiteDatabase db) {
        Question q1 = new Question("World War I began in which year?", "1923",
                "1938", "1917", "1914", "D");
        this.addQuestion(q1, db);

        Question q2 = new Question("Adolf Hitler was born in which country?",
                "France", "Germany", "Austria", "Hungary", "C");
        this.addQuestion(q2, db);

        //add more questions
    }

    // addding new questions to db
    public void addQuestion(Question question, SQLiteDatabase db) {
        ContentValues values = new ContentValues();
        values.put(QUESTIONS, question.getQuestion());
        values.put(ANSWER, question.getAnswer());
        values.put(OPTIONA, question.getOptionA());
        values.put(OPTIONB, question.getOptionB());
        values.put(OPTIONC, question.getOptionC());
        values.put(OPTIOND, question.getOptionD());

        db.insert(TABLE_NAME, null, values);
    }

    public List<Question> getAllQuestions() {
        List<Question> questionList = new ArrayList<Question>();

        String query = "SELECT * FROM " + TABLE_NAME;
        dba = this.getReadableDatabase();
        Cursor cursor = dba.rawQuery(query, null);

        if (cursor.moveToFirst()) {
            do {
                Question quest = new Question();
                quest.setID(cursor.getInt(0));
                quest.setQuestion(cursor.getString(1));
                quest.setAnswer(cursor.getString(2));
                quest.setOptionA(cursor.getString(3));
                quest.setOptionB(cursor.getString(4));
                quest.setOptionC(cursor.getString(5));
                quest.setOptionD(cursor.getString(6));

                questionList.add(quest);

            } while (cursor.moveToNext());
        }

        cursor.close();
        dba.close();
        return questionList;
    }

    public int rowCount() {
        int row = 0;
        String query = "SELECT * FROM " + TABLE_NAME;
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query, null);
        row = cursor.getCount();

        cursor.close();
        return row;
    }
}

Did you change the `onCreate`, `addQuestions` and `addQuestion` methods? You should be using `db.insert` not `dba.insert` — Evin1_, Jul 11 '16 at 01:19
You don't need to instantiate it, you are getting a reference to as an argument in the `onCreate` method. The code above just passes that reference through the `addQuestions` and `addQuestion` methods. — Evin1_, Jul 11 '16 at 02:00

score 1 · Answer 2 · answered Jul 11 '16 at 05:53

Change your insertion method by below,

   public void addQuestion(Question question)  
   {
        dba = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(QUESTIONS, question.getQuestion());
        values.put(ANSWER, question.getAnswer());
        values.put(OPTIONA, question.getOptionA());
        values.put(OPTIONB, question.getOptionB());
        values.put(OPTIONC, question.getOptionC());
        values.put(OPTIOND, question.getOptionD());

        dba.insert(TABLE_NAME, null, values);
   }

score 0 · Answer 3 · answered Jul 11 '16 at 00:59

0

dba returns null because you create your database with db. So use db.insert instead.

answered Jul 11 '16 at 00:59

Alexandre Martin

1,472
5
14
27

I can't use db because db is for the onCreate method only to create the table. – Nasim Ahmed Jul 11 '16 at 01:16

score 0 · Answer 4 · answered Jul 11 '16 at 04:07

I think this may because dba never be initialized before. Try to add question from main activity (WorldHistory.java). Like this:

DatabaseHandler handler = new DatabaseHandler(this); 
SQLiteDatabase db = handler.getWritableDatabase();

and then use this db to invoke the insert() method

More information: https://developer.android.com/training/basics/data-storage/databases.html#WriteDbRow

Android SQLite Quiz App

4 Answers4