ViewPager2 not able to dynamically add remove fragment

问题

Removing/Adding fragments at index results in unexpected behaviour in Viewpager2. This was not possible with ViewPager but expected to work with Viewpager2. It causes duplicate fragments and out of sync TabLayout. Here is a demo project which reproduces this issue. There is a toggle button which removes a fragment and reattaches it at a particular index. In this case attached fragment should be green but it's blue and there are 2 blue fragments somehow.

here is how my adapter looks

class ViewPager2Adapter(activity: FragmentActivity) : FragmentStateAdapter(activity) {
    val fragmentList: MutableList<FragmentName> = mutableListOf()

    override fun getItemCount(): Int {
        return fragmentList.size
    }

    override fun createFragment(position: Int): Fragment {
        return when (fragmentList[position]) {
            FragmentName.WHITE -> WhiteFragment()
            FragmentName.RED -> RedFragment()
            FragmentName.GREEN -> GreenFragment()
            FragmentName.BLUE -> BlueFragment()
        }
    }

    fun add(fragment: FragmentName) {
        fragmentList.add(fragment)
        notifyDataSetChanged()
    }

    fun add(index: Int, fragment: FragmentName) {
        fragmentList.add(index, fragment)
        notifyDataSetChanged()
    }

    fun remove(index: Int) {
        fragmentList.removeAt(index)
        notifyDataSetChanged()
    }

    fun remove(name: FragmentName) {
        fragmentList.remove(name)
        notifyDataSetChanged()
    }

    enum class FragmentName {
        WHITE,
        RED,
        GREEN,
        BLUE
    }
}

I have filed a bug with google as well

回答1:

Turns out that you need to override these two methods if you are working with mutable collections in ViewPager2

override fun getItemId(position: Int): Long {
        return fragmentList[position].ordinal.toLong()
    }

    override fun containsItem(itemId: Long): Boolean {
        val fragment = FragmentName.values()[itemId.toInt()]
        return fragmentList.contains(fragment)
    }

Adding these two in my current adapter fixes the problem

来源：https://stackoverflow.com/questions/61406176/viewpager2-not-able-to-dynamically-add-remove-fragment