Android Retrofit with RxJava to fetch data asyncronously


Example

From the GitHub repo of RxJava, RxJava is a Java VM implementation of Reactive Extensions: a library for composing asynchronous and event-based programs by using observable sequences. It extends the observer pattern to support sequences of data/events and adds operators that allow you to compose sequences together declaratively while abstracting away concerns about things like low-level threading, synchronisation, thread-safety and concurrent data structures.

Retrofit is a type-safe HTTP client for Android and Java, using this, developers can make all network stuff much more easier. As an example, we are going to download some JSON and show it in RecyclerView as a list.

Getting started:

Add RxJava, RxAndroid and Retrofit dependencies in your app level build.gradle file: compile "io.reactivex:rxjava:1.1.6"
compile "io.reactivex:rxandroid:1.2.1"
compile "com.squareup.retrofit2:adapter-rxjava:2.0.2"
compile "com.google.code.gson:gson:2.6.2"
compile "com.squareup.retrofit2:retrofit:2.0.2"
compile "com.squareup.retrofit2:converter-gson:2.0.2"

Define ApiClient and ApiInterface to exchange data from server

public class ApiClient {

private static Retrofit retrofitInstance = null;
private static final String BASE_URL = "https://api.github.com/";

public static Retrofit getInstance() {
    if (retrofitInstance == null) {
        retrofitInstance = new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create())
                .build();
    }
    return retrofitInstance;
}

public static <T> T createRetrofitService(final Class<T> clazz, final String endPoint) {
    final Retrofit restAdapter = new Retrofit.Builder()
            .baseUrl(endPoint)
            .build();

    return restAdapter.create(clazz);
}

public static String getBaseUrl() {
    return BASE_URL;
}}

public interface ApiInterface {

@GET("repos/{org}/{repo}/issues")
Observable<List<Issue>> getIssues(@Path("org") String organisation,
                                  @Path("repo") String repositoryName,
                                  @Query("page") int pageNumber);}

Note the getRepos() is returning an Observable and not just a list of issues.

Define the models

An example for this is shown. You can use free services like JsonSchema2Pojo or this.

public class Comment {

@SerializedName("url")
@Expose
private String url;
@SerializedName("html_url")
@Expose
private String htmlUrl;

//Getters and Setters
}

Create Retrofit instance

ApiInterface apiService = ApiClient.getInstance().create(ApiInterface.class);

Then, Use this instance to fetch data from server

Observable<List<Issue>> issueObservable = apiService.getIssues(org, repo,                 pageNumber);
    issueObservable.subscribeOn(Schedulers.newThread())
            .observeOn(AndroidSchedulers.mainThread())
            .map(issues -> issues)    //get issues and map to issues list
            .subscribe(new Subscriber<List<Issue>>() {
                @Override
                public void onCompleted() {
                    Log.i(TAG, "onCompleted: COMPLETED!");
                }

                @Override
                public void onError(Throwable e) {
                    Log.e(TAG, "onError: ", e);
                }

                @Override
                public void onNext(List<Issue> issues) {
                    recyclerView.setAdapter(new IssueAdapter(MainActivity.this, issues, apiService));
                }
            });

Now, you have successfully fetched data from a server using Retrofit and RxJava.