How can I wait for an object filled asynchronously in Android UI thread without blocking it?

Issue

I have a singleton to handle the registration and elimination of an entity Profilo ( a Profile).

This entity is set by passing an identifier and gathering information on the server in an async way.

My problem is that when I have to return my instance of profilo if it's not still loaded it will return null.

public class AccountHandler {
    private static AccountHandler istanza = null;

    Context context;
    private boolean logged;
    private Profilo profilo;


    private AccountHandler(Context context) {
        this.context = context;
        //initialization
        //setting logged properly
            assignField(this.getName());
        }
    }

    public static AccountHandler getAccountHandler(Context context) {
        if (istanza == null) {
            synchronized (AccountHandler.class) {
                if (istanza == null) {
                    istanza = new AccountHandler(context);
                }
            }
        }
        return istanza;
    }

    public void setAccount(String nickname, String accessingCode) {
        logged = true;
        assignField(nickname);
    }

    //other methods

    private void assignField(String nickname) {
        ProfiloClient profiloClient = new ProfiloClient();
        profiloClient.addParam(Profilo.FIELDS[0], nickname);
        profiloClient.get(new JsonHttpResponseHandler() {
            @Override
            public void onSuccess(int statusCode,
                                  Header[] headers,
                                  JSONArray response) {
                JSONObject objson = null;
                try {
                    objson = (JSONObject) response.getJSONObject(0);
                } catch (JSONException e) {
                    e.printStackTrace();
                }
                AccountHandler accountHandler = AccountHandler.getAccountHandler(context);
    // Profilo is created with a JSONObject
    // **setProfilo is called in async**
                **accountHandler.setProfilo(new Profilo(objson));**
            }

        });
    }


    private void setProfilo(Profilo profilo) {
        this.profilo = profilo;
    }



    public Profilo getProfilo() {
        if( logged && profilo == null)
            //How can I wait that profilo is loaded by the JsonHttpResponseHandler before to return it

        return this.profilo;
    }


}

Solution

Instead of calling getProfilo you could use a callback mechanism in which the AccountHandler class notifies the caller when the profile has been loaded. e.g.

  public void setAccount(String nickname, String accessingCode, MyCallback cb) {
      assignField(nickname, cb);
  }
  private void assignField(String nickname, MyCallback cb) {
      ....
      accountHandler.setProfilo(new Profilo(objson));
      cb.onSuccess(this.profilo);
  }

Create an inner Interface MyCallback (rename it) in your AccountHandler class

public class AccountHandler {
    public interface MyCallback {
        void onSuccess(Profilo profile);
    }
}

Now whenever you call setAccount you will pass the callback and get notified when the profile is available e.g.

accountHandler.setAccount("Test", "Test", new AccountHandler.MyCallback() {
        void onSuccess(Profilio profile) {
            // do something with the profile
        }
    }

Answered By - Murat Karagöz