升级我从assets文件夹复制的sqlite数据库(Android)

我从assets文件夹复制数据库并将其复制到我的设备(或模拟器).一切都是正确的.我在DDMS透视图中看到了我的数据库.但是我想要升级我的数据库,所以我做了：

super(context,db_name,null,2); //changed version from 1 to 2

并修改onUpgrade方法：

@Override
public void onUpgrade(sqliteDatabase db,int oldVersion,int newVersion) {
    if(newVersion > oldVersion){
        this.myContext.deleteDatabase(db_name);
        try {
            this.copyDataBase();
        } catch (IOException E) {
            e.printStackTrace();
        }
    }
}

但运行后我的设备上仍然有旧版本的数据库.我如何删除旧版本的数据库并复制新的. db_name是我的数据库名称(格式,但不是路径),copyDataBase()是将数据库复制到设备的方法(它的工作原理).

我粘贴我的所有代码：

public class DataBaseHelper extends sqliteOpenHelper{

    private static String DB_PATH = "/data/data/sitcom.quiz/databases/";

    private static String db_name = "sitcoms.sqlite";

    private sqliteDatabase myDataBase; 

    private final Context myContext;

    public DataBaseHelper(Context context) {

        super(context,4);
        this.myContext = context;
    }   

    public void createDataBase() throws IOException{

        Boolean dbExist = checkDataBase();

        if(dbExist){
            //do nothing - database already exist
        }else{

            this.getReadableDatabase();

            try {

                copyDataBase();

            } catch (IOException E) {

                throw new Error("Error copying database");

            }
        }

    }

    private Boolean checkDataBase(){

        sqliteDatabase checkDB = null;

        try{
            String myPath = DB_PATH + db_name;
            checkDB = sqliteDatabase.openDatabase(myPath,sqliteDatabase.oPEN_READONLY);

        }catch(sqliteException E){
            //database does't exist yet.
        }

        if(checkDB != null){
            checkDB.close();
        }

        return checkDB != null ? true : false;
    }


    private void copyDataBase() throws IOException{

        //Open your local db as the input stream
        InputStream myInput = myContext.getAssets().open(db_name);

        // 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);

        //transfer bytes from the inputfile to the outputfile
        byte[] buffer = new byte[1024];
        int length;
        while ((length = myInput.read(buffer))>0){
            myOutput.write(buffer,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,sqliteDatabase.oPEN_READONLY);

    }

    @Override
    public synchronized void close() {

            if(myDataBase != null)
                myDataBase.close();

            super.close();

    }

    @Override
    public void onCreate(sqliteDatabase db) {

    }

    @Override
    public void onUpgrade(sqliteDatabase db,int newVersion) {
        Log.d("adas","dasd");

        if(newVersion > oldVersion){
            String myPath = DB_PATH + db_name;
            this.myContext.deleteDatabase(myPath);
            try {
                this.copyDataBase();
            } catch (IOException E) {
                e.printStackTrace();
            }
        }
    }


}

和我的活动：

DataBaseHelper myDbHelper = new DataBaseHelper(this);
        myDbHelper = new DataBaseHelper(this);

        try {
            myDbHelper.createDataBase();
        } catch (IOException ioE) {
            throw new Error("Unable to create database");
        }
        try {
            myDbHelper.openDataBase();
        }catch(SQLException sqlE){
            throw sqle;
        }

谢谢,如果你能给我理由或只是暗示为什么这不起作用.