游标在sqlite中返回null

Question

我的方法getHighScore（）中的光标返回一个空值，我不知道为什么。我用过

system.out.println(cursor.moveToFirst());

并打印错误。当我在SQLiteman中运行查询时，它返回一个结果。

这是我全班同学。我把伪数据放入包中。

public class DatabaseHandler extends SQLiteOpenHelper{

// Static Database Information
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "quiz_db.db";
public final static String DATABASE_PATH = "/data/data/com.example.app/databases/quiz_db.db";
private static final String QUESTION_TABLE = "Questions";
private static final String SCORE_TABLE = "Score";

// Questions Table Column Names
private static final String Q_ID = "id";
private static final String Q_QUESTION = "question";
private static final String Q_ANSWER1 = "answer_one";
private static final String Q_ANSWER2 = "answer_two";
private static final String Q_ANSWER3 = "answer_three";
private static final String Q_ANSWER4 = "answer_four";
private static final String Q_CORRECT = "correct_answer";


// Score Table Column Names
private static final String S_ID = "id";
private static final String S_SCORE = "score";

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

// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_QUESTION_TABLE = "CREATE TABLE " + QUESTION_TABLE + "("
            + Q_ID + " INTEGER PRIMARY KEY," + Q_QUESTION + " TEXT,"
            + Q_ANSWER1 + " TEXT" + Q_ANSWER2 + " TEXT" + Q_ANSWER3 + " TEXT" + Q_ANSWER4 + " TEXT" + Q_CORRECT + " TEXT" + 
            ")";

    String CREATE_SCORE_TABLE = "CREATE TABLE " + SCORE_TABLE + "("
            + S_ID + " INTEGER," + S_SCORE + " INTEGER"
            + ")";


    db.execSQL(CREATE_QUESTION_TABLE);
    db.execSQL(CREATE_SCORE_TABLE);
}

// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + QUESTION_TABLE);

    db.execSQL("DROP TABLE IF EXISTS " + SCORE_TABLE);
    // Create tables again
    onCreate(db);
}

// Get High Score
public int getHighScore () {
    int score = 0;
    String query = "SELECT score FROM " + SCORE_TABLE + ";";
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(query, null);
    if (cursor != null && cursor.moveToFirst()) {
         score = cursor.getInt(cursor.getColumnIndex("score"));
    }

    cursor.close();
    return score;

}

我的数据库位于“assets”文件夹中，文件名为“quiz_db.db”