预填充数据库的游标计数始终为0

Question

我有一个预填充的资产数据库。我在第一次启动后复制了该数据库并尝试查询，但是cursor从未有数据。它显示了所选table的所有列，但getCount()始终为0。我的错误在哪里？这是我的代码：

public class DataBaseHelper extends SQLiteOpenHelper {
    private Context mycontext;
    private String DB_PATH;    
    private static String DB_NAME = "championBuilds.db";//the extension may be .sqlite or .db
    public SQLiteDatabase myDataBase;   

    public DataBaseHelper(Context context) throws IOException, SQLException {
        super(context,DB_NAME,null,1);
        this.mycontext=context;
        DB_PATH = "/data/data/com.app.myapp/databases/";
        boolean dbexist = checkdatabase();
        if (dbexist) {
            //System.out.println("Database exists");
            opendatabase();
        } else {
            System.out.println("Database doesn't exist");
            createdatabase();
        }
    }

    public void createdatabase() throws IOException {
        boolean dbexist = checkdatabase();
        if(dbexist) {
            //System.out.println(" Database exists.");
        } else {
            this.getReadableDatabase();
            try {
                copydatabase();
            } catch(IOException e) {
                throw new Error("Error copying database");
            }
        }
    }   

    private boolean checkdatabase() {
        //SQLiteDatabase checkdb = null;
        boolean checkdb = false;
        try {
            String myPath = DB_PATH + DB_NAME;
            File dbfile = new File(myPath);
            //checkdb = SQLiteDatabase.openDatabase(myPath,null,SQLiteDatabase.OPEN_READWRITE);
            checkdb = dbfile.exists();
        } catch(SQLiteException e) {
            System.out.println("Database doesn't exist");
        }
        return checkdb;
    }

    private void copydatabase() throws IOException {
        // Path to the just created empty db
        String outfilename = DB_PATH + DB_NAME;

        //Open the empty db as the output stream
        OutputStream myoutput = new FileOutputStream(outfilename);

        //Open your local db as the input stream
        InputStream myinput = mycontext.getAssets().open(DB_NAME);

        // transfer byte to inputfile to outputfile
        byte[] buffer = new byte[1024];
        int length;
        while ((length = myinput.read(buffer))>0) {
            myoutput.write(buffer,0,length);
        }

        //Close the streams
        myoutput.flush();
        myoutput.close();
        myinput.close();
    }

    public void opendatabase() throws SQLException {
        //Open the database
        String mypath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(mypath, null, SQLiteDatabase.OPEN_READWRITE);
    }

    public synchronized void close() {
        if(myDataBase != null) {
            myDataBase.close();
        }
        super.close();
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {

    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }

    public List<Book> getAllBooks() {
        List<Book> books = new ArrayList();
        String selectQuery = "SELECT * FROM Books";
        Cursor cursor = myDataBase.rawQuery(selectQuery, null);
        //if TABLE has rows
        if (cursor.moveToFirst()) {
            //Loop through the table rows
            do {
                Book book = new Book();
                book.id = cursor.getInt(0);
                book.setTitle(cursor.getString(1));
                book.setAuthor(cursor.getString(2));

                // Add book to books
                books.add(book);
            } while (cursor.moveToNext());
        }
        myDataBase.close();
        return books;
    }
}

还有我怎么称呼这些方法：

try {
    db = new DataBaseHelper(this);
    List<Book> books = db.getAllBooks();
} catch (IOException e) {
    e.printStackTrace();
} catch (SQLException e) {
    e.printStackTrace();
}