How to make multiple request and wait until data is come from all the requests in retrofit 2.0 - android

Question

current code:

Retrofit retrofit = new Retrofit.Builder()
                  .baseUrl(Constant.BASEURL)
                  .addConverterFactory(GsonConverterFac         


        

Answer 1

The clean and neat approach to wait until all your requests will be done is to use Retrofit2 in conjunction with RxJava2 and its zip function.

What zip does is basically constructs new observable that waits until all your retrofit Observable requests will be done and then it will emit its own result.

Here is an example Retrofit2 interface with Observables:

public interface MyBackendAPI {
  @GET("users/{user}")
  Observable getUser(@Path("user") String user);

  @GET("users/{user}/photos")
  Observable> listPhotos(@Path("user") String user);

  @GET("users/{user}/friends")
  Observable> listFriends(@Path("user") String user);
}

In the code where you going to make multiple requests and only after all of them will complete do something else you can then write the following:

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl("https://api.example.com/")
            .build();

    MyBackendAPI backendApi = retrofit.create(MyBackendAPI.class);

    List> requests = new ArrayList<>();

    // Make a collection of all requests you need to call at once, there can be any number of requests, not only 3. You can have 2 or 5, or 100.
    requests.add(backendApi.getUser("someUserId"));
    requests.add(backendApi.listPhotos("someUserId"));
    requests.add(backendApi.listFriends("someUserId"));

    // Zip all requests with the Function, which will receive the results.
    Observable.zip(
            requests,
            new Function() {
                @Override
                public Object apply(Object[] objects) throws Exception {
                    // Objects[] is an array of combined results of completed requests

                    // do something with those results and emit new event
                    return new Object();
                }
            })
            // After all requests had been performed the next observer will receive the Object, returned from Function
            .subscribe(
                    // Will be triggered if all requests will end successfully (4xx and 5xx also are successful requests too)
                    new Consumer