Question

I think I might be on the wrong track here so I’m posting this to find out.

I’m developing an android app that uses a number of rest-service requests to load its data.

I arranged my code following the n-tier pattern: domain layer (domain) / webservice access layer (dal) / business logic layer (service) / ui layer (ui)

From my activity I start an AsyncTask to load the items from the service layer. While the items are loading I show a progress dialog with a continious looping circle icon. This isn’t very user friendly, so I would like to display progress in stead via a progress indicator.

I can easily alter my dal so that it first gets a list of id’s of the items to fetch, and then fetches them one at a time, in stead of in bulk. This way I could report progress to the user, while updating the ui everytime a new item (or 2 or more) is loaded.

The problem is that I don’t know how to go about this. All the examples of AsyncTask work on the principle that everything happens within a class that inherits AsyncTask and this has to be executed from the ui thread.

Is there anyone who can provide a short code example on how I should define my AsyncTask class, and how I would be able to report progress from within the data access layer to the UI?

If I put all the code in the ui, there would be no problem, but that’s not very good practice imo.

Code example of what I want to do:

Somewhere in MainApplication I keep a list of orders:

public List<Order> orders = null;

My activity calls the AsyncTask and starts it:

OrderActivity.java

public void loadOrdersAsync() {
    // Create async task instance
    OrderLoaderAsyncTask loader = new OrderLoaderAsyncTask();

    // Start loading
    loader.doInBackground();
}

OrderLoadAsyncTask.java

public class OrderLoaderAsyncTask  extends AsyncTask {
    @Override
    public Integer doInBackground(Context.... params) {
        OrderService service = new OrderService();
        MainApplication.orders = service.getAll();
    }

    @Override
    public void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);

        // Update progress bar
        updateProgressBar(values);
    }
}

OrderService.java

public class OrderService {
    public List<Order> getAll() {
        // Check to see if we have a cached version
        // If we don't, we fetch the orders from REST webservice
        OrderRepository repository = new OrderRepository();

        // Get list of ID's to fetch
        List<Integer> ids = new ArrayList<Integer>;
        List<Order> orders = new ArrayList<Order>;
        ids = repository.getIDs();

        // For each id, fetch order from webservice
        for (Integer id : ids) {
            Order order = repository.getOneById(id);

            orders.add(order);

            // Report progress, but how?
        }

        return orders;
    }
}

Now in my service I can keep track of the progress, but how do I report this progress to the UI without moving the logic to build the orderslist to my AsyncTask class? How do I report progress from within my service layer? Or even from within my repository layer?

Answer 1

I don’t see a way of doing that with precision, REST services are kind of request-reply, you’ll receive data only after its all loaded in data layer inside REST server.

I’ll do it with a progress bar, updating each 500mS with a Timer. Just have in mind that Timer fires another thread, so you need to update UI inside a runOnUiThread() method of your activity.

Example code:

public class myActivity extends Activity {

    private Timer myTimer;

    @Override
    public void onCreate(Bundle b) {
        super.onCreate(b);
        setContentView(R.layout.main);

        myTimer = new Timer();
        myTimer.schedule(new TimerTask() {
            @Override
            public void run() {
                TimerMethod();
            }

        }, 0, 500);  // 500mS starting with no delay
    }

    private void TimerMethod()
    {
            // this runs each time Timer fires
        this.runOnUiThread(Timer_Tick);
    }

    private Runnable Timer_Tick = new Runnable() {
        public void run() {

            // do something with my progress bar
        UpdateMyProgressBar();

        }
    };
}