Unlimited/Dynamic ViewPager in both directions

Question

There is one use-case of ViewPager I\'ve never seen pretty implemented.

ViewPager is more or less static structure. It\'s not so hard to add Pa

Answer 1

Using negative position values stands very far from natural order of ViewPager usage and is not the Adapter issue at all. Please have a look into the source code of ViewPager in the support package source in Android SDK. For example, here is a setCurrentItemInternal private implementation:

void setCurrentItemInternal(int item, boolean smoothScroll, boolean always, int velocity) {
    if (mAdapter == null || mAdapter.getCount() <= 0) {
        setScrollingCacheEnabled(false);
        return;
    }
    if (!always && mCurItem == item && mItems.size() != 0) {
        setScrollingCacheEnabled(false);
        return;
    }

    if (item < 0) {
        item = 0;
    } else if (item >= mAdapter.getCount()) {
        item = mAdapter.getCount() - 1;
    }
    final int pageLimit = mOffscreenPageLimit;
    if (item > (mCurItem + pageLimit) || item < (mCurItem - pageLimit)) {
        // We are doing a jump by more than one page.  To avoid
        // glitches, we want to keep all current pages in the view
        // until the scroll ends.
        for (int i=0; i<mItems.size(); i++) {
            mItems.get(i).scrolling = true;
        }
    }
    final boolean dispatchSelected = mCurItem != item;
    populate(item);
    scrollToItem(item, smoothScroll, velocity, dispatchSelected);
}

As you can see, ViewPager explicitly assumes no negative position values.

Answer 2

Will this help,

public static class MyAdapter extends FragmentPagerAdapter {
    public MyAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public int getCount() {
        return Integer.MAX_VALUE;
    }

    @Override
    public Fragment getItem(int position) {
        return getFragmentBasedOnPosition(position);
    }

    private Fragment getFragmentBasedOnPosition(int position) {
        int fragmentPos = position % 3; // Assuming you have 3 fragments
        switch(fragmentPos) {
            case 1:
            return Fragment1.newInstance();
            case 2:
            return Fragment2.newInstance();
            case 3:
            return Fragment3.newInstance();
        }
    }
}

and then,

mPager.setCurrentItem((int)(Integer.MAX_VALUE/2)); // assuming mPager is your ViewPager