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containsItem覆盖和getItemIdin的目的是什么FragmentStateAdapter？

如果将新列表传递给FragmentStatePagerAdapter实现并调用，是否需要这些覆盖notifyDataSetChanged？

从文档中，如果基础数据集正在更改，则似乎两个覆盖都是必需的，并且您需要调用notifyDataSetChanged?

/**
 * Default implementation works for collections that don't add, move, remove items.
 * <p>
 * TODO(b/122670460): add lint rule
 * When overriding, also override {@link #getItemId(int)}
 */
public boolean containsItem(long itemId) {
    return itemId >= 0 && itemId < getItemCount();
}

/**
 * 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;
}

例如，这是我的实现

class MyAdapter(host : Fragment) : FragmentStateAdapter(host) {

    data class FragItem(val newInstance : () -> Fragment, val fragId : Long)

    private var fragments = mapOf<Integer,FragItem>()

    override fun createFragment(position: Int): Fragment {
        return fragments[position]?.newInstance?.invoke() ?: DefaultFragment()
    }
    
    fun applyDataSet(newFragments : Map<Integer, FragItem>) {
        fragments = newFragments
        notifyDataSetChanged()
    }

    override fun getItemCount() = fragments.size

    override fun containsItem(itemId: Long): Boolean{
        return fragments.any { it.value.fragId == itemId }
    }

    override fun getItemId(position: Int) : Long{
        return fragments.values.elementAt(position).fragId
    }
}

现在我可以摆脱getItemIdand了containsItem吗？还是离开他们？怎么样getItemCount？

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1 回答 1

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  • getItemCount将指示回收者要渲染多少个项目。当前索引将被传递position到createFragment，所以很明显你需要它
  • 如果您想为您的回收商提供稳定的 ID，则可以使用getItemId并实施。containsItem拥有稳定的 ID 允许进行某些优化，通常是当它涉及对列表中不相邻的元素的操作时。
于 2021-07-14T18:00:00.293 回答