CyclePagerAdapter Example

CyclePagerAdapter.java

public abstract class CyclePagerAdapter<T> extends PagerAdapter implements ViewPager.OnPageChangeListener {
    protected List<T> mItemList = null;
    private WeakReference<CycleViewPager> mViewPagerRef = null;

    public CyclePagerAdapter(@NonNull List<T> list, @NonNull CycleViewPager cycleViewPager) {
        if (list.size() <= 1) {
            // needn't to support infinite cycle
            mItemList = new ArrayList<>(list);
        } else {
            // refer: https://maniacdev.com/2013/08/tutorial-how-to-create-an-infinite-scrolling-uicollectionview
            mItemList = new ArrayList<>(ArrayUtils.getLengthSafe(list) + 2);
            mItemList.add(list.get(ArrayUtils.getLengthSafe(list) - 1));
            mItemList.addAll(list);
            mItemList.add(list.get(0));
        }

        cycleViewPager.addOnPageChangeListener(this);
        mViewPagerRef = new WeakReference<>(cycleViewPager);
    }

    public boolean isCycleEnable() {
        return getCount() > 1;
    }

    protected boolean isFakePosition(@IntRange(from = 0) int position) {
        if (isCycleEnable()) {
            return position == 0 || position == ArrayUtils.getLengthSafe(mItemList) - 1;
        }
        return false;
    }

    public int getCyclePosition(@IntRange(from = 0) int actualPosition) {
        int cyclePosition = actualPosition;
        if (isCycleEnable()) {
            cyclePosition = (cyclePosition - 1) % (getCount() - 2);
        }
        return cyclePosition;
    }

    @Override
    public int getCount() {
        return ArrayUtils.getLengthSafe(mItemList);
    }

    @CallSuper
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        // no operation
    }

    @CallSuper
    @Override
    public void onPageSelected(int position) {
        // no operation
    }

    @CallSuper
    @Override
    public void onPageScrollStateChanged(int state) {
        if (mViewPagerRef == null || mViewPagerRef.get() == null || !isCycleEnable()) {
            return;
        }

        CycleViewPager viewPager = mViewPagerRef.get();
        if (viewPager.getCurrentItem() == getCount() - 1) {
            viewPager.post(new Runnable() {
                @Override
                public void run() {
                    if (mViewPagerRef == null || mViewPagerRef.get() == null) {
                        return;
                    }
                    ViewPager viewPager = mViewPagerRef.get();
                    if (viewPager.getCurrentItem() == getCount() - 1) {
                        viewPager.setCurrentItem(1, false);
                    }
                }
            });
        } else if (viewPager.getCurrentItem() == 0) {
            viewPager.post(new Runnable() {
                @Override
                public void run() {
                    if (mViewPagerRef == null || mViewPagerRef.get() == null) {
                        return;
                    }
                    ViewPager viewPager = mViewPagerRef.get();
                    if (viewPager.getCurrentItem() == 0) {
                        viewPager.setCurrentItem(getCount() - 2, false);
                    }
                }
            });
        }
    }
}