Android : Implementation of two way Endless Viewpager

Question

What I want:

I have been trying to implement two directional Endless viewpager in Android, Left to Right & Right to Left

What I did:

I have implemented Endless viewpager adapter, it works fine for right to left direction, I have set current item position by viewPager.setCurrentItem(Integer.MAX_VALUE/2);.

Reference:

Help would be appreciate.

Answer 1

One simple way to achieve this for ViewPager2 is with 3 basic ideas:

1. Add the first and last items of your data model collection to the end and start, respectively, of that same collection. E.g. listOf(1, 2, 3, 4, 5) should become listOf(5, 1, 2, 3, 4, 5, 1).
2. When setting up the pager, set it to start with index 1.
3. When the user scrolls to index 0, have the pager scroll instantly to the penultimate index. When the user scrolls to the last index, have the pager scroll instantly to index 1.

Some sample code to do this is as follows:

1.

private fun <T> List<T>.prepareForTwoWayPaging(): List<T> {
    val first = first()
    val last = last()
    return toMutableList().apply {
        add(0, last)
        add(first)
    }
}

pager.setCurrentItem(1, false)

pager.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {
    override fun onPageScrolled(
        position: Int,
        positionOffset: Float,
        positionOffsetPixels: Int
    ) {
        // We're only interested when the pager offset is exactly centered. This
        // will help create a convincing illusion of two-way paging.
        if (positionOffsetPixels != 0) {
            return
        }
        when (position) {
            0 -> pager.setCurrentItem(adapter.itemCount - 2, false)
            adapter.itemCount - 1 -> pager.setCurrentItem(1, false)
        }
    }
})

Caveat: this code does not reconcile any TabLayout or an empty data model collection.