MainActivity.java

package sample.github.nisrulz.usingrxjava;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.TextView;
import com.google.gson.Gson;
import java.io.IOException;
import java.util.Map;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import rx.Observable;
import rx.Subscriber;
import rx.Subscription;
import rx.android.schedulers.AndroidSchedulers;
import rx.functions.Func0;
import rx.schedulers.Schedulers;

public class MainActivity extends AppCompatActivity {

    private Subscription subscription;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        subscription = getGistObservable()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Subscriber<Gist>() {
                    @Override
                    public void onCompleted() {

                    }

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

                    @Override
                    public void onNext(Gist gist) {
                        StringBuilder sb = new StringBuilder();
                        // Output
                        for (Map.Entry<String, GistFile> entry : gist.files.entrySet()) {
                            sb.append(entry.getKey());
                            sb.append(" - ");
                            sb.append("Length of file ");
                            sb.append(entry.getValue().content.length());
                            sb.append("\n");
                        }

                        TextView text = (TextView) findViewById(R.id.main_message);
                        text.setText(sb.toString());

                    }
                });
    }


    @Override
    protected void onDestroy() {
        super.onDestroy();

        if (subscription != null && !subscription.isUnsubscribed()) {
            subscription.unsubscribe();
        }
    }

    @Nullable
    private Gist getGist() throws IOException {

        OkHttpClient client = new OkHttpClient();

        // Go get this Gist: https://gist.github.com/donnfelker/db72a05cc03ef523ee74
        // via the GitHub API
        Request request = new Request.Builder()
                .url("https://api.github.com/gists/637e5d11e6d00c35090c99b5d85ba01d")
                .build();

        Response response = client.newCall(request).execute();

        if (response.isSuccessful()) {
            Gist gist = new Gson().fromJson(response.body().charStream(), Gist.class);
            return gist;
        }
        return null;
    }


    public Observable<Gist> getGistObservable() {
        return Observable.defer(new Func0<Observable<Gist>>() {
            @Override
            public Observable<Gist> call() {
                try {
                    return Observable.just(getGist());
                } catch (IOException e) {
                    return null;
                }
            }
        });

    }
}