// MainActivity
public class MainActivity extends AppCompatActivity implements ImageListFragment.OnGalleryImageSelected {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (savedInstanceState == null) {
            getSupportFragmentManager()
                    .beginTransaction()
                    .add(R.id.root_layout, ImageListFragment.newInstance(), "galleryImageList")
                    .commit();
        }
    }
    @Override
    public void OnGalleryImageSelected(int imageResId) {
        final ImageDetailFragment detailsFragment = ImageDetailFragment.newInstance(imageResId);
        getSupportFragmentManager()
                .beginTransaction()
                .replace(R.id.root_layout, detailsFragment, "galleryImageDetails")
                .addToBackStack(null)
                .commit();
    }

}

// ImageDetailFragment

public class ImageDetailFragment extends Fragment {
    private static final String IMAGE_ID = "imageResId";

    public static ImageDetailFragment newInstance(int imageResId) {

        final Bundle args = new Bundle();
        args.putInt(IMAGE_ID, imageResId);
        final ImageDetailFragment fragment = new ImageDetailFragment();
        fragment.setArguments(args);
        return fragment;
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        final View view = inflater.inflate(R.layout.fragment_image_details, container, false);
        final ImageView imageView = (ImageView) view.findViewById(R.id.gallery_image);
        final Bundle args = getArguments();
        imageView.setImageResource(args.getInt(IMAGE_ID));
        return view;
    }

}

// ImageListFragment

public class ImageListFragment extends Fragment {
    private int[] mImageResIds;
    private OnGalleryImageSelected mListener;
    public static ImageListFragment newInstance() {
        return new ImageListFragment();
    }
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);

        mListener = (OnGalleryImageSelected) context;

        final Resources resources = context.getResources();
        final TypedArray typedArray = resources.obtainTypedArray(R.array.images);
        final int imageCount = 18;
        mImageResIds = new int[imageCount];
        for (int i = 0; i < imageCount; i++) {
            mImageResIds[i] = typedArray.getResourceId(i, 0);
        }
        typedArray.recycle();
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        final View view = inflater.inflate(R.layout.fragment_image_list, container, false);

        final Activity activity = getActivity();
        final RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
        recyclerView.setLayoutManager(new LinearLayoutManager(activity));
        recyclerView.setAdapter(new GalleryImageAdapter(activity));
        return view;
    }

    class GalleryImageAdapter extends RecyclerView.Adapter<ViewHolder> {

        private LayoutInflater mLayoutInflater;

        public GalleryImageAdapter(Context context) {
            mLayoutInflater = LayoutInflater.from(context);
        }

        @Override
        public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
            return new ViewHolder(mLayoutInflater
                    .inflate(R.layout.recycler_view, viewGroup, false));
        }

        @Override
        public void onBindViewHolder(ViewHolder viewHolder, final int position) {

            final int imageResId = mImageResIds[position];

            viewHolder.setData(imageResId);
            viewHolder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    System.out.println("sending to pager");
                    System.out.println(position);
                    Intent intent = FooPager.newIntent(getActivity(),position);
                    startActivity (intent);
                   // mListener.OnGalleryImageSelected(imageResId);
                }
            });
        }

        @Override
        public int getItemCount() {
            return mImageResIds.length;
        }
    }

    class ViewHolder extends RecyclerView.ViewHolder {
        private ImageView mImageView;
        private ViewHolder(View itemView) {
            super(itemView);
            mImageView = (ImageView) itemView.findViewById(R.id.gallery_image);

        }
        private void setData(int imageResId) {
            mImageView.setImageResource(imageResId);
        }
    }
    public interface OnGalleryImageSelected {
        void OnGalleryImageSelected(int imageResId);
    }
}

// FooPager

public class FooPager extends FragmentActivity{
    public static final String EXTRA_IMAGE_ID = "meow";
    public static int id = 0;
    private ViewPager mViewPager;
    private Integer images [] = {
            R.drawable.a, R.drawable.b,R.drawable.c,R.drawable.d,R.drawable.e,
            R.drawable.f, R.drawable.g, R.drawable.h,R.drawable.i,R.drawable.j,
            R.drawable.k, R.drawable.l, R.drawable.m,R.drawable.n,R.drawable.o,
            R.drawable.p, R.drawable.q, R.drawable.r
    };

    public static Intent newIntent(Context packageContext, int id) {
        Intent intent = new Intent(packageContext,FooPager.class);
        intent.putExtra(EXTRA_IMAGE_ID,id);
        id = id;
        return intent;
    }

    @Override
    protected void onCreate (Bundle savedInstanceState) {
        super.onCreate (savedInstanceState);
        setContentView(R.layout.activity_image_pager);
        mViewPager = (ViewPager) findViewById (R.id.activity_image_pager_view_pager);

        FragmentManager fragmentManager = getSupportFragmentManager ();
        mViewPager.setAdapter(new FragmentStatePagerAdapter(fragmentManager) {
            @Override
            public Fragment getItem(int position) {

                System.out.println(images[position]);
                int id = images[position];
                return ImageDetailFragment.newInstance(id);
            }

            @Override
            public int getCount() {
                return images.length;
            }
        });

        for (int i=0; i < images.length; i++) {
            if(images[i] == id) {
                mViewPager.setCurrentItem(i);
                break;
            }
        }
        }
    }

// AndroidManifest

  <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".FooPager"
            android:label="@string/app_name">
        </activity>
    </application>