android - 删除 viewPager2 中的 fragment 使用 FragmentStateAdapter，但仍显示

Question

我有viewPager2和FragmentStateAdapter，还有Fragement1、2,3 4，我在fragment2，想去掉fragment3，在fragment2之后显示fragment4。
问题是它总是显示 fragment 3(数据)，调试显示 fragment 3已被删除，但显示的页面仍然有 fragment 3内容。

适配器:

class TipsAdapter(
private val items: MutableList<TripPage>,
context: FragmentActivity
) : FragmentStateAdapter(context) {

private val fragmentFactory = context.supportFragmentManager.fragmentFactory
private val classLoader = context.classLoader

override fun getItemCount(): Int = items.size

override fun createFragment(position: Int): Fragment {
    val pageInfo = items[position]
    val fragment = fragmentFactory.instantiate(classLoader, pageInfo.fragmentClass.name)
    fragment.arguments = Bundle().also { it.putParcelable(PAGE_INFO, pageInfo) }
    return fragment
}

fun getFragmentName(position: Int) = items[position].fragmentClass.simpleName

fun removeFragment(position: Int) {
    items.removeAt(position)
    notifyItemRemoved(position)
    notifyItemRangeChanged(position, items.size)
    notifyDataSetChanged()
}

}

删除 fragment 代码:

      if ((view_pager.adapter as TipsAdapter).getFragmentName(index + 1).equals(
            TripPreFragment::class.simpleName) &&
            viewModel.shouldRemoveBulkApply()) {
            (view_pager.adapter as TipsAdapter).removeFragment(index + 1)
            view_pager.setCurrentItem(index + 1, true)
        } else {
            view_pager.setCurrentItem(index + 1, true)
        }

Answer 1

最后，它对我有用。当我们调用 notifyDataSetChanged() , android 会调用
方法getItemId()在适配器中，检查项目是否已更新。它返回源代码中的位置。这意味着在列表 0..i..n , 如果您删除 i , 变为 0...i...n-1 , i不会改变，数据也不会在 adater 中更新。

    /**
 * Default implementation works for collections that don't add, move, remove items.
 * <p>
 * TODO(b/122670460): add lint rule
 * When overriding, also override {@link #containsItem(long)}.
 * <p>
 * If the item is not a part of the collection, return {@link RecyclerView#NO_ID}.
 *
 * @param position Adapter position
 * @return stable item id {@link RecyclerView.Adapter#hasStableIds()}
 */
@Override
public long getItemId(int position) {
    return position;
}

你需要做的是重写这个方法和 containsItem(long) ,
就我而言，我使用每个 fragment 的哈希码:

class TipsAdapter(
     private val items: MutableList<TripPreferencesOptimizerPage>,
     context: FragmentActivity
    ) : FragmentStateAdapter(context) {

private val fragmentFactory = context.supportFragmentManager.fragmentFactory
private val classLoader = context.classLoader
private val pageIds= items.map { it.hashCode().toLong() }

override fun getItemCount(): Int = items.size

override fun createFragment(position: Int): Fragment {
    val pageInfo = items[position]
    val fragment = fragmentFactory.instantiate(classLoader, pageInfo.fragmentClass.name)
    fragment.arguments = Bundle().also { it.putParcelable(PAGE_INFO, pageInfo) }
    return fragment
}

fun getFragmentName(position: Int) = items[position].fragmentClass.simpleName

fun removeFragment(position: Int) {
    items.removeAt(position)
    notifyItemRangeChanged(position, items.size)
    notifyDataSetChanged()
}

override fun getItemId(position: Int): Long {
    return items[position].hashCode().toLong() // make sure notifyDataSetChanged() works
}

override fun containsItem(itemId: Long): Boolean {
    return pageIds.contains(itemId)
}
}