workaround for request with activity and screen orientation changes

OrientationChangeWithPendingNetworkRequestActivity.java

/**
 * @author Lukasz Marczak
 * @since 28.09.16.
 */
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;
import android.widget.ProgressBar;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.util.concurrent.Callable;

import retrofit.RestAdapter;
import retrofit.client.Response;
import retrofit.http.GET;
import retrofit.http.Path;
import retrofit.mime.TypedInput;
import rx.Observable;
import rx.Subscriber;
import rx.android.schedulers.AndroidSchedulers;
import rx.schedulers.Schedulers;
import rx.subjects.ReplaySubject;
import rx.subjects.Subject;
import rx.subscriptions.CompositeSubscription;

public class OrientationChangeWithPendingNetworkRequestActivity extends AppCompatActivity {

    public static final String TAG = OrientationChangeWithPendingNetworkRequestActivity.class.getSimpleName();

    Subject<Bitmap, Bitmap> pendingRequest;
    CompositeSubscription compositeSubscription = new CompositeSubscription();

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

        final ImageView imageView = (ImageView) findViewById(R.id.imageView);
        final ProgressBar progressBar = (ProgressBar) findViewById(R.id.progressBar);

        boolean isFirstRequest = isFirstRequest();

        pendingRequest = retrievePendingRequestOrCreateNew();

        if (isFirstRequest) {

            String url = "your-url-to-large-bitmap-" +
                    "you-won't-lose-pending-request-because" +
                    "you-retain-request-inside-subject";

            getBitmapImpl(url).subscribe(pendingRequest);
        } else {
            //already subscribed, result is already inside Subject
            //called when screen is rotated, we won't request twice
        }
        progressBar.setVisibility(View.VISIBLE);

        rx.Subscription subscription = pendingRequest.observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Subscriber<Bitmap>() {
                    @Override
                    public void onCompleted() {
                        Log.d(TAG, "onCompleted: ");
                    }

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

                    @Override
                    public void onNext(Bitmap bitmap) {
                        Log.d(TAG, "onNext: ");
                        progressBar.setVisibility(View.GONE);
                        imageView.setImageBitmap(bitmap);
                    }
                });
        compositeSubscription.add(subscription);
    }

    @Override
    protected void onDestroy() {
        Log.d(TAG, "onDestroy: ");
        //not sure I should clear this
       // if (!compositeSubscription.isUnsubscribed()) compositeSubscription.unsubscribe();
        super.onDestroy();
    }

    @SuppressWarnings("unchecked")
    Subject<Bitmap, Bitmap> retrievePendingRequestOrCreateNew() {
        Object lastPendingRequest = getLastCustomNonConfigurationInstance();
        if (lastPendingRequest == null) {
            return createSubject();
        } else {
            return (Subject<Bitmap, Bitmap>) lastPendingRequest;
        }
    }

    Subject<Bitmap, Bitmap> createSubject() {
        return ReplaySubject.create();
    }

    @Override
    public Object onRetainCustomNonConfigurationInstance() {
        return pendingRequest;
    }

    static Observable<Bitmap> getBitmapImpl(final String url) {
        return Observable.fromCallable(new Callable<Bitmap>() {
            @Override
            public Bitmap call() throws Exception {
                String[] pieces = url.split("/");
                String query = pieces[pieces.length - 1];
                String endpoint = url.replace("/" + query, "");

                RestAdapter adapter = new RestAdapter.Builder().setEndpoint(endpoint).build();
                ImagesAPI api = adapter.create(ImagesAPI.class);

                Response blockingResponse = api.getImage(query);

                TypedInput input = blockingResponse.getBody();

                Bitmap bitmap = null;
                try {
                    BufferedInputStream stream = new BufferedInputStream(input.in());
                    bitmap = BitmapFactory.decodeStream(stream);
                    stream.close();
                } catch (IOException e) {
                    Log.e(TAG, "failed to decode stream");
                    e.printStackTrace();
                }
                return bitmap;
            }
        }).subscribeOn(Schedulers.newThread());
    }
    public interface ImagesAPI {
        @GET("/{path}")
        Response getImage(@Path("path") String subString);
    }
    boolean isFirstRequest() {
        return getLastCustomNonConfigurationInstance() == null;
    }
}