Best practice to implement Retrofit callback to recreated activity?

Question

I'm switching to Retrofit and trying to understand proper architecture for using it with async callbacks.

For example I have an interface:

interface RESTService{     @GET("/api/getusername")     void getUserName(@Query("user_id") String userId,                       Callback<Response> callback); } 

And I run this from main activity:

RestAdapter restAdapter = new RestAdapter.Builder()         .setServer("WEBSITE_URL")              .build(); RESTService api = restAdapter.create(RESTService.class); api.getUserName(userId, new Callback<Response> {...}); 

Then user rotates the device and I have newly created activity... What was happen here? How can I get response to the new activity (I assume that api call in background will execute longer than first activity life). Maybe I must use static instance of callback or what? Please show me the right way...

Answer 1

Use otto. There are a lot of samples to mix otto and retrofit, for example https://github.com/pat-dalberg/ImageNom/blob/master/src/com/dalberg/android/imagenom/async/FlickrClient.java

Or read this post http://www.mdswanson.com/blog/2014/04/07/durable-android-rest-clients.html It answers on almost all questions

Answer 2

For potential long running server calls i use an AsyncTaskLoader. For me, the main advantage of Loaders are the activity-lifecycle handling. onLoadFinished is only called if your activity is visible to the user. Loaders are also shared between activity/fragment and orientation changes.

So i created an ApiLoader which uses retrofits synchronous calls in loadInBackground.

abstract public class ApiLoader<Type> extends AsyncTaskLoader<ApiResponse<Type>> {      protected ApiService service;     protected ApiResponse<Type> response;      public ApiLoader(Context context) {         super(context);         Vibes app = (Vibes) context.getApplicationContext();         service = app.getApiService();     }      @Override     public ApiResponse<Type> loadInBackground() {         ApiResponse<Type> localResponse = new ApiResponse<Type>();          try {             localResponse.setResult(callServerInBackground(service));         } catch(Exception e) {             localResponse.setError(e);         }          response = localResponse;         return response;     }      @Override     protected void onStartLoading() {         super.onStartLoading();         if(response != null) {             deliverResult(response);         }          if(takeContentChanged() || response == null) {             forceLoad();         }     }      @Override     protected void onReset() {         super.onReset();         response = null;     }       abstract protected Type callServerInBackground(SecondLevelApiService api) throws Exception;  } 

In your activity you init this loader like this:

getSupportLoaderManager().initLoader(1, null, new LoaderManager.LoaderCallbacks<ApiResponse<DAO>>() {         @Override         public Loader<ApiResponse<DAO>> onCreateLoader(int id, Bundle args) {             spbProgress.setVisibility(View.VISIBLE);              return new ApiLoader<DAO>(getApplicationContext()) {                 @Override                 protected DAO callServerInBackground(ApiService api) throws Exception {                     return api.requestDAO();                 }             };         }          @Override         public void onLoadFinished(Loader<ApiResponse<DAO>> loader, ApiResponse<DAO> data) {             if (!data.hasError()) {                 DAO dao = data.getResult();                 //handle data             } else {                 Exception error = data.getError();                 //handle error             }         }          @Override         public void onLoaderReset(Loader<ApiResponse<DAO>> loader) {}     }); 

If you want to request data multiple times use restartLoader instead of initLoader.