SQLiteOpenHelper“onCreate”没有被调用？ （数据库不存在）

从片段中我以这种方式实例化

fmdata = new FileManagerData(getActivity());

下面的课。我不明白为什么 onCreate() 没有被调用并且我的数据库没有被创建。

public class FileManagerData {
public static final String TAG = FileManagerData.class.getSimpleName();;


Context context;
DBHelper dbHelper;

public FileManagerData (Context context){
    this.context = context;
    dbHelper = new DBHelper();
}

private class DBHelper extends SQLiteOpenHelper{

    private static final String DB_NAME = "filename.db";
    private static final String DB_SQL = "filename.sql";
    private static final int DB_VERSION = 1; // internal number

    public DBHelper() {
        super(context, DB_NAME, null, DB_VERSION);  
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
            // this is NEVER called and my DB does not exist yet
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }   
}

EDIT

The onCreate method 将在第一次访问数据库后调用。向数据库进行查询并onCreate将被调用。