SQLite Android . unable to open database file

I found a lot of question about this problem, but i can't fix it. I have a sqlite db in assets folder:

assets/data/data/{package_name}/databases/mydb.db

I can open database and read data before change one table structure. I try to uninstall the app and reinstall again, but i get the same exception.

What can i do now?

Thanks in advance

EDIT

// The Android's default system path of your application database.
private static String DB_PATH = "/data/data/{mypagackename}/databases/";

private static String DB_NAME = "mydb.db";

Open database (Before change table structure, adding some fields, it doesn't work)

public void openDataBase() throws SQLException {

    // Open the database
    String myPath = DB_PATH + DB_NAME;
    myDataBase = SQLiteDatabase.openDatabase(myPath, null,
            SQLiteDatabase.OPEN_READONLY);

}