Android ViewPager - Show preview of page on left and right

Question

I\'m using Android\'s ViewPager. What I want to do is to show a preview of the page on both the left and the right. I\'ve seen where I can use a negative

Answer 1

Solution with the new ViewPager2

Nowadays you should consider using ViewPager2 which "replaces ViewPager, addressing most of its predecessor’s pain-points":

• Based on RecyclerView
• RTL (right-to-left) layout support
• Vertical orientation support
• Reliable Fragment support (including handling changes to the underlying Fragment collection)
• Dataset change animations (including DiffUtil support)

The result

The code

In your Activity/Fragment, setup the ViewPager2:

// MyRecyclerViewAdapter is an standard RecyclerView.Adapter :)
viewPager2.adapter = MyRecyclerViewAdapter() 

// You need to retain one page on each side so that the next and previous items are visible
viewPager2.offscreenPageLimit = 1

// Add a PageTransformer that translates the next and previous items horizontally
// towards the center of the screen, which makes them visible
val nextItemVisiblePx = resources.getDimension(R.dimen.viewpager_next_item_visible)
val currentItemHorizontalMarginPx = resources.getDimension(R.dimen.viewpager_current_item_horizontal_margin)
val pageTranslationX = nextItemVisiblePx + currentItemHorizontalMarginPx
val pageTransformer = ViewPager2.PageTransformer { page: View, position: Float ->
    page.translationX = -pageTranslationX * position
    // Next line scales the item's height. You can remove it if you don't want this effect
    page.scaleY = 1 - (0.25f * abs(position))
    // If you want a fading effect uncomment the next line:
    // page.alpha = 0.25f + (1 - abs(position))
}
viewPager2.setPageTransformer(pageTransformer)

// The ItemDecoration gives the current (centered) item horizontal margin so that
// it doesn't occupy the whole screen width. Without it the items overlap
val itemDecoration = HorizontalMarginItemDecoration(
    context,
    R.dimen.viewpager_current_item_horizontal_margin
)
viewPager2.addItemDecoration(itemDecoration)

Add the HorizontalMarginItemDecoration, which is a trivial ItemDecoration:

/**
 * Adds margin to the left and right sides of the RecyclerView item.
 * Adapted from https://stackoverflow.com/a/27664023/4034572
 * @param horizontalMarginInDp the margin resource, in dp.
 */
class HorizontalMarginItemDecoration(context: Context, @DimenRes horizontalMarginInDp: Int) :
    RecyclerView.ItemDecoration() {

    private val horizontalMarginInPx: Int =
        context.resources.getDimension(horizontalMarginInDp).toInt()

    override fun getItemOffsets(
        outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State
    ) {
        outRect.right = horizontalMarginInPx
        outRect.left = horizontalMarginInPx
    }

}

Add the dimensions that control how much of the previous/next item is visible, and current item horizontal margin:

26dp
42dp

Finally add the ViewPager2 to your layout:

One important thing: a ViewPager2 item must have layout_height="match_parent" (otherwise it throws an IllegalStateException), so you should do something like:

PageTransformer examples

Google has added a guide on ViewPager2 that has 2 PageTransformer implementations that you can use as an inspiration: https://developer.android.com/training/animation/screen-slide-2

About the new ViewPager2

• Announcement at Google I/O 2019
• Documentation
• Release notes
• Code sample
• Migrate from ViewPager to ViewPager2