Android ViewPager adapter - force getPageWidth every time

Question

I have two fragments in ViewPager, my requirement is to show some portion of the second fragment with in the first fragment for the first time to give the user some idea that there is one more page. Once the user swipes to next page and comes back to first, the first fragment should occupy full screen(not just 90%). So I've kept a flag to check whether it's first time or not and returning right pageWidth -

public float getPageWidth(int position) {
    if (position == 0 && isPatiallyShowNextItem) {
        return 0.9f;
    }
    isPatiallyShowNextItem = false;
    return 1f;
}

The problem is getPageWidth() is called only once and the first fragment is always occupying only 90% of screen, How can I force getPageWidth when the user swipes to next fragment or let the first fragment occupy 100% of screen when user moves to second page afterwards. FYI - I've tried below calls after changing the flag but nothing worked!

pagerAdapter.notifyDataSetChanged();
viewPager.requestLayout();
viewPager.invalidate();

Answer 1

A simple approach would be to use a ViewPager.PageTransformer. do something like this to achieve the 90% page reveal effect

public class PageRevealTransformer implements ViewPager.PageTransformer
{

    @Override
    public void transformPage(View page, float position)
    {
        int pageWidth = page.getWidth();
        if (position < -.9)
        {
            // TODO: do something when this condition is certisfied
        } else if (position <= .5)
        {
            float newPageWidth = pageWidth / 3;
            page.setTranslationX(newPageWidth * -(position));
        } else
        {
            // TODO: do something when this condition is certified
        }
    }
}

and apply to your page adapter like this

viewPager.setPageTransformer(true, new PageRevealTransformer());

get your logic around this and you are good to go. you can also view a full documentation of usage on http://developer.android.com/training/animation/screen-slide.html