Question

I want to call CRUD operations on Order objects in my Activity. I was wondered is the following implementation of a “Service” class a good way to do this? I don’t want any reference to DatabaseHelper or DAO objects in my Activity code as I don’t think this would be desireable.
Here is my Service class

public class OrderService 
{
    private static OrderService instance;
    private static Dao<Order, Integer> orderDAO;


    static public void init(Context ctx) {
        if (null == instance) {
            instance = new OrderService(ctx);
        }
    }

    public static OrderService getInstance() {
        return instance;
    }

    private OrderService(Context ctx) {
        DatabaseHelper helper = DatabaseHelper.getInstance(ctx);
        helper.getWritableDatabase();
        orderDAO = helper.getOrderDao();
    }

    public Order getOrderWithId(int orderId) {
        Order myOrder = null;
        try {
            myOrder = orderDAO.queryForId(orderId);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return myOrder;
    }

    public Order neworder(Order order) {
        try {
            orderDAO.create(order);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return order;
    }

    public void deleteorder(Order order) {
        try {
            orderDAO.delete(order);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public void updateorder(Order order) {
        try {
            orderDAO.update(order);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public List <Order> getordersForCategory(int orderId) {
        List <Order> orders = null;
        try {
            orders = orderDAO.queryForAll();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return orders;
    }
}

and here is how I intend to use the service

public class OrderProcessingActivity extends Activity {

    int orderID;
    private Order order;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.myview);
        order = OrderService.getInstance().getOrderWithId(orderID);
        ......

Does this look like a good way to access the SQLlite DB ?
I have read about “Service” implementations that can be configured in Android so I was sondered is this something that I should be using instead?

Answer 1

Despite moving your database logic to a different class, you’re doing all of your database operations in the UI thread, which is not ideal. Also note that even though your class is called “service” it doesn’t inherit from any of the Service classes in Android.

One alternate approach would be to do your database operations from the doInBackground method of an AsyncTask, return your needed data from that method. Then, use the returned data to update your activity in the onPostExecute method.