Android SQLite Quiz App

Question

Я пытаюсь создать приложение, которое позволяет вам пройти викторину, например, викторину мировой истории. В основном действии пользователь нажимает кнопку ввода, чтобы выбрать категорию викторины, допустим, мы выбираем всемирную историю, тогда она должна идти на мировую историю, но она падает. Вот мой код до сих пор не знаю, что случилось с ним:

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++; 
    } 
}  

Это сообщение об ошибке:

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) 

Answer 1

Используйте этот DatabaseHandler вместо:

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; 
    } 
} 

Answer 2

dba возвращает null, так как вы создаете базу данных с db. Поэтому используйте db.insert.

Answer 3

Я думаю, что это может потому, что дБА никогда не будет инициализирован раньше. Попробуйте добавить вопрос из основного вида деятельности (WorldHistory.java). Как это:

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

, а затем использовать этот дб для вызова вставки() метод

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

Answer 4

Изменить ваш метод вставки по ниже,

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); 
    }