ViewPager OnAdapterChangeListener设置第一页

Question

I am trying to build a circular ViewPager where I don't have to make any settings from the outside. In order for this ViewPager to have circular scrolling, I need to put a copy of the last image at the start (index 0) and a copy of the first image at the end. This mean that my ViewPager has to start at index 1, not index 0. I can easily do this from the outside by calling viewPager.setCurrentItem(1) , but I want to encapsulate this in the PagerAdapter itself.

My problem is finding an appropriate callback method to do that. It doesn't work in the constructor of the PagerAdapter .

One way that seems to work is by adding an OnAdapterChangeListener like in my code below. Is that legit or will I run into trouble?

public class CircularViewPagerAdapter extends PagerAdapter {
private Context context;
private List<String> imageUrls;
private int lastIndex;
private int position = 1;

CircularViewPagerAdapter(Context context, final ViewPager viewPager, List<String> imageUrls) {
    this.context = context;
    this.imageUrls = imageUrls;
    if (imageUrls.size() > 1) {
        imageUrls.add(0, imageUrls.get(imageUrls.size() - 1));
        imageUrls.add(imageUrls.get(1));
        lastIndex = imageUrls.size() - 1;
    }

    viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {
            CircularViewPagerAdapter.this.position = position;
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            if (position == 0) viewPager.setCurrentItem(lastIndex - 1, false);
            if (position == lastIndex) viewPager.setCurrentItem(1, false);
        }
    });

    viewPager.addOnAdapterChangeListener(new ViewPager.OnAdapterChangeListener() {
        @Override
        public void onAdapterChanged(@NonNull ViewPager viewPager, @Nullable PagerAdapter oldAdapter, @Nullable PagerAdapter newAdapter) {
            viewPager.setCurrentItem(1);
        }
    });
}

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

@Override
public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
    return view == object;
}

@NonNull
@Override
public Object instantiateItem(@NonNull final ViewGroup container, int position) {
    ImageView imageView = new ImageView(context);
    Picasso.get()
            .load(imageUrls.get(position))
            .fit()
            .centerCrop()
            .into(imageView);
    container.addView(imageView);

    return imageView;
}

@Override
public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
    container.removeView((View) object);
}
}

Answer 1

For achieving the Circle View Pager i have found the solution here. you just have to customize the View pager by using the below classes from SOURCE HERE

InfinitePagerAdapter.java,  
InfiniteViewPager.java,  
RecycleBin.java,   
RecyclingPagerAdapter.java 

After that use InfinitePagerAdapter instant of PagerAdapter .