Validate login using sqlite database by making objects in Android

I am trying to develop an android application that let users login using their name and password already exists in the database. I tried solution on the following link:

Using SQlite to validate Logins in Android

It works for me but the issue is that the code works only once i get into the project by editing the Manifest file and replacing the login activity by some other activity. I mean it works when the project creates the database in its DDMS. Otherwise it never allows login on any new emulator and device. I am using my database tables in assets folder.

My SqlHelper class is:

public class SqlHelper extends SQLiteOpenHelper implements DatabaseMetaData
{   
public static SQLiteDatabase dbSqlite;
protected SQLiteDatabase db = null;

private final Context myContext;

public SqlHelper(Context context) {
    super(context, DATABASE_NAME, null, 1);
    this.myContext = context;

}


public void onCreate(SQLiteDatabase db) {
    // check if exists and copy database from resource
    createDB();

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    Log.w("SqlHelper", "Upgrading database from version " + oldVersion
            + " to " + newVersion + ", which will destroy all old data");
    onCreate(db);
}

public void createDatabase() {
    createDB();
}

private void createDB() {

    boolean dbExist = DBExists();

    if (!dbExist) {
        copyDBFromResource();
    }
}

private boolean DBExists() {

    SQLiteDatabase db = null;

    try {
        String databasePath = DATABASE_PATH + DATABASE_NAME;
        db = SQLiteDatabase.openDatabase(databasePath, null,
                SQLiteDatabase.OPEN_READWRITE);
        db.setLocale(Locale.getDefault());
        db.setLockingEnabled(true);
        db.setVersion(1);

    } catch (SQLiteException e) {

        Log.e("SqlHelper", "database not found");

    }

    if (db != null) {

        db.close();

    }

    return db != null ? true : false;
}

private void copyDBFromResource() {

    InputStream inputStream = null;
    OutputStream outStream = null;
    String dbFilePath = DATABASE_PATH + DATABASE_NAME;

    try {

        inputStream = myContext.getAssets().open(DATABASE_NAME);

        outStream = new FileOutputStream(dbFilePath);

        byte[] buffer = new byte[1024];
        int length;
        while ((length = inputStream.read(buffer)) > 0) {
            outStream.write(buffer, 0, length);
        }

        outStream.flush();
        outStream.close();
        inputStream.close();

    } catch (IOException e) {

        throw new Error("Problem copying database from resource file.");

    }

}

public void openDataBase() throws SQLException {

    String myPath = DATABASE_PATH + DATABASE_NAME;
    dbSqlite = SQLiteDatabase.openDatabase(myPath, null,
            SQLiteDatabase.OPEN_READWRITE);

}


@Override
public synchronized void close() {

    if (db开发者_如何学运维Sqlite != null)
        dbSqlite.close();

    super.close();

}
   }

My DatabaseMetaData Interface Class is :

    public interface DatabaseMetaData {
String DATABASE_PATH = "/data/data/com.dbApp/databases/";

String DATABASE_NAME = "dbApp";

    String TABLE_USERLIST = "UserList";
String TABLE_CUSTOMER = "Customer";


//UserList
String COLUMN_USER_NAME = "User_Name";
String COLUMN_PASSWORD = "Password";

    //Customer
String COLUMN_ID = "_id";
String COLUMN_LISTID = "ListID";
String COLUMN_NAME = "Name";
String COLUMN_COMPANYNAME = "CompanyName";
String COLUMN_FIRSTNAME = "FirstName";
String COLUMN_LASTNAME = "LastName";
    }

And in LoginActivity i use the following method:

 protected boolean tryLogin(String username, String password)
{
    try{
        Cursor cursor = null;
        cursor = db.rawQuery("select " + DatabaseMetaData.COLUMN_PASSWORD + " from " + DatabaseMetaData.TABLE_USERLIST + " where " + DatabaseMetaData.COLUMN_USER_NAME + " = " + "'" +username+ "'", null);

        //cursor = db.rawQuery("select password from UserList where user_name='" + username + "'", null);
        if (cursor.moveToFirst()) {
            String str = cursor.getString(0);
            if (password.equals(str)) {
                cursor.close();
                return true;

            }else{

                return false;
            }
        }cursor.close();
    }

Please help me..