android waiting for response from server

Question

say I want to perform an Http request from the server, this process takes time.

now because of this, the http request needs to be run on a different thread (AsyncTask, Runnable, etc.)

but sometimes I just need the response when I ask for it, in order to update the UI

using Thread.sleep in a loop to wait for the response is not good performance wise

example: I want the user's name, I ask the server for it, and I have to wait for it now the activity calls the UserManager that calls the serverHandler that performs the operation and returns the result back

maybe an event system is in order, but I'm not sure how to do this in my scenerio and quite frankly I am really confused on this issue

please help someone?

Answer 1

This can most definitely be done w/ AsyncTask... Handle the network request in doInBackground() and once doInBackground() is finished, onPostExecute() is triggered on the UI thread and that's where you can execute any code that will update UI elements.

If you need something a bit more generic and re-usable, you would probably want to implement a callback... I'll refer to the UI thread as the client and the AsyncTask as the server.

1. Create a new interface and create some method stubs.

   public interface MyEventListener {
       public void onEventCompleted();
       public void onEventFailed();
   } 
   

2. Have your client pass instance of MyEventListener to the server. A typical way of doing this is to have your client implement the interface (MyEventListener) and pass itself to the server.

   public class MyActivity implement MyEventListener {
   
       public void startEvent() {
           new MyAsyncTask(this).execute();
       }           
   
       @Override
       public void onEventCompleted() {
           // TODO
       }
   
       @Override
       public void onEventFailed() {
           // TODO
       }
   }
   

3. On the onPostExecute of the server, check if the callback is null and call the appropriate method.

   public class MyAsyncTask extends AsyncTask<Void, Void, Void> {
       private MyEventListener callback;
   
       public MyAsyncTask(MyEventListener cb) {
           callback = cb;
       }
   
       [...]
   
       @Override
       protected void onPostExecute(Void aVoid) {
           if(callback != null) {
               callback.onEventCompleted();
           }
       }
   }
   

You can read more about callbacks here: http://www.javaworld.com/javaworld/javatips/jw-javatip10.html