问题描述

在索引处删除/添加片段会导致 Viewpager2 出现意外行为.这对于 ViewPager 是不可能的，但预计可以与 Viewpager2 一起使用.它会导致重复片段和不同步 TabLayout.这是一个重现此问题的演示项目.有一个切换按钮可以删除片段并将其重新附加到特定索引处.在这种情况下，附加的片段应该是绿色的，但它是蓝色的，并且不知何故有 2 个蓝色片段.

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.

这是我的适配器的外观

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
    }
}

我也向 google 提交了 错误

I have filed a bug with google as well

推荐答案

如果你在 ViewPager2 中使用 mutable 集合，你需要重写这两个方法

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)
    }

在我当前的适配器中添加这两个可以解决问题

Adding these two in my current adapter fixes the problem

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