删除 viewPager2 中的片段使用 FragmentStateAdapter，但仍显示

remove fragment in viewPager2 use FragmentStateAdapter, but still display(删除 viewPager2 中的片段使用 FragmentStateAdapter，但仍显示)

问题描述

我有viewPager2和FragmentStateAdapter，还有Fragment1,2,3 4，我在fragment2，想去掉fragment3，在fragment2之后显示fragment4.问题是它总是显示片段3(数据)，调试显示片段3已被删除，但显示的页面仍然有片段3内容.

I have a viewPager2 and FragmentStateAdapter, and there are Fragement1, 2,3 4, I am in fragment2, and want to remove fragment3, and display fragment4 after fragment2. The problem is it always show me fragment3(data), the debug shows the fragment3 has been removed, but the displayed page still has fragment3 content.

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()
}

}

删除片段代码:

      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)
        }

推荐答案

最后，它对我有用.当我们调用 notifyDataSetChanged() 时，android 会调用适配器中的 getItemId() 方法，用于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 中，如果您删除 i ，它将变为 0...i...n-1，i 不会改变，adater 中的数据也不会更新.

Finally, it works for me. when we call notifyDataSetChanged(), android will call method getItemId() in adapter, to check if the item has been updated or not. it returns the position in source code. which means in list 0..i..n, if you remove i , it becomes to 0...i...n-1, the i won't change and the data won't update in adater.

    /**
 * 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),

what you need to do is rewrite this method and containsItem(long),

就我而言，我使用每个片段的哈希码:

for my case, I use the hashcode of each fragment:

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)
}
}

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