Einstellung der Bilder aus url in ViewPager Android

Ich bin nach dieses tutorial für die Umsetzung ViewPager in meinem Projekt. Ich habe das getan, mit statische Bilder erfolgreich. Jetzt will ich es ändern, so, die Bilder sind entnommen aus urls und angezeigt ViewPager. Unten ist mein code.

Wo sollte ich hinzufügen, dass die Methode zum herunterladen von Bildern und wie Sie es
zu meiner ViewPager?

Jede Hilfe wird sehr geschätzt.

MainActivity:

public class MainActivity extends AppCompatActivity {

    private ArrayList<Integer> images;
    private BitmapFactory.Options options;
    private ViewPager viewPager;
    private View btnNext, btnPrev;
    private FragmentStatePagerAdapter adapter;
    private LinearLayout thumbnailsContainer;
    private final static int[] resourceIDs = new int[]{R.mipmap.a, R.mipmap.b,
            R.mipmap.c, R.mipmap.d, R.mipmap.e, R.mipmap.f, R.mipmap.g};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        images = new ArrayList<>();

        //find view by id
        viewPager = (ViewPager) findViewById(R.id.view_pager);
        thumbnailsContainer = (LinearLayout) findViewById(R.id.container);
        btnNext = findViewById(R.id.next);
        btnPrev = findViewById(R.id.prev);

        btnPrev.setOnClickListener(onClickListener(0));
        btnNext.setOnClickListener(onClickListener(1));

        setImagesData();

        //init viewpager adapter and attach
        adapter = new ViewPagerAdapter(getSupportFragmentManager(), images);
        viewPager.setAdapter(adapter);

        inflateThumbnails();
    }

    private View.OnClickListener onClickListener(final int i) {
        return new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (i > 0) {
                    //next page
                    if (viewPager.getCurrentItem() < viewPager.getAdapter().getCount() - 1) {
                        viewPager.setCurrentItem(viewPager.getCurrentItem() + 1);
                    }
                } else {
                    //previous page
                    if (viewPager.getCurrentItem() > 0) {
                        viewPager.setCurrentItem(viewPager.getCurrentItem() - 1);
                    }
                }
            }
        };
    }

    private void setImagesData() {
        for (int i = 0; i < resourceIDs.length; i++) {
            images.add(resourceIDs[i]);
        }
    }

    private void inflateThumbnails() {
        for (int i = 0; i < images.size(); i++) {
            View imageLayout = getLayoutInflater().inflate(R.layout.item_image, null);
            ImageView imageView = (ImageView) imageLayout.findViewById(R.id.img_thumb);
            imageView.setOnClickListener(onChagePageClickListener(i));
            options = new BitmapFactory.Options();
            options.inSampleSize = 3;
            options.inDither = false;
            Bitmap bitmap = BitmapFactory.decodeResource(getResources(), images.get(i), options );
            imageView.setImageBitmap(bitmap);
            //set to image view
            imageView.setImageBitmap(bitmap);
            //add imageview
            thumbnailsContainer.addView(imageLayout);
        }
    }

    private View.OnClickListener onChagePageClickListener(final int i) {
        return new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                viewPager.setCurrentItem(i);
            }
        };
    }
}

PageFragment Klasse:

   public class PageFragment extends Fragment {

        private int imageResource;
        private Bitmap bitmap;

        public static PageFragment getInstance(int resourceID) {
            PageFragment f = new PageFragment();
            Bundle args = new Bundle();
            args.putInt("image_source", resourceID);
            f.setArguments(args);
            return f;
        }

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            imageResource = getArguments().getInt("image_source");
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            return inflater.inflate(R.layout.fragment_page, container, false);
        }

        @Override
        public void onViewCreated(View view, Bundle savedInstanceState) {
            super.onViewCreated(view, savedInstanceState);
            ImageView imageView = (ImageView) view.findViewById(R.id.image);

            BitmapFactory.Options o = new BitmapFactory.Options();
            o.inSampleSize = 4;
            o.inDither = false;
            bitmap = BitmapFactory.decodeResource(getResources(), imageResource, o);
            imageView.setImageBitmap(bitmap);
        }

        @Override
        public void onDestroy() {
            super.onDestroy();
            bitmap.recycle();
            bitmap = null;
        }
    }

ViewPager Adapter class:

public class ViewPagerAdapter extends FragmentStatePagerAdapter {

    private List<Integer> images;

    public ViewPagerAdapter(FragmentManager fm, List<Integer> imagesList) {
        super(fm);
        this.images = imagesList;
    }

    @Override
    public Fragment getItem(int position) {
        return PageFragment.getInstance(images.get(position));
    }

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