使用 ItemTouchHelper 拖动项目时 RecyclerView 滚动到顶部 [英] RecyclerView scrolls to top when dragging item with ItemTouchHelper

问题描述

我有一个奇怪的错误，每当我开始在其中拖动项目时，我的 RecyclerView 就会滚动回顶部位置.如果有任何区别，它在 ViewPager 内.您可以在 .gif 附件中看到行为.

当 notifyItemMoved 被调用时，RecyclerView 视图似乎滚动到顶部，并且它滚动到第一个视图至少部分显示在屏幕上.>

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适配器

class AccountListAdapter(私有 val onAccountClickListener: OnAccountClickListener) :ListAdapter(AccountDiffCallback()){覆盖乐趣 onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {val inflater = LayoutInflater.from(parent.context)返回 ViewHolder(充气机.inflate(R.layout.view_account_list_item，家长，错误的))}覆盖 fun getItemId(position: Int): Long {返回 getItem(position).accountId.toLong()}覆盖乐趣 onBindViewHolder(holder: ViewHolder, position: Int) {holder.bind(getItem(position), onAccountClickListener)}class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView), OnItemDragged {有趣的绑定(帐户:帐户，onAccountClickListener:OnAccountClickListener){itemView.account_name.text = account.nameitemView.setOnClickListener {onAccountClickListener.onAccountClick(账户)}}覆盖乐趣 onItemSelected() {itemView.setBackgroundColor(ContextCompat.getColor(itemView.context,R.color.background_contrast))}覆盖乐趣 onItemClear() {itemView.setBackgroundColor(ContextCompat.getColor(itemView.context,R.color.background))}}类 AccountDiffCallback : DiffUtil.ItemCallback() {覆盖乐趣 areItemsTheSame(oldItem: Account, newItem: Account): Boolean {返回 oldItem.accountId == newItem.accountId}覆盖乐趣 areContentsTheSame(oldItem: Account, newItem: Account): Boolean {返回 (oldItem.balance == newItem.balance&&oldItem.annualReturn == newItem.annualReturn&&oldItem.name == newItem.name)}}接口 OnAccountClickListener {有趣的 onAccountClick(帐户:帐户)}接口 OnItemDragged {有趣的 onItemSelected()有趣的 onItemClear()}}

ItemTouchHelper

 私人乐趣 setupListAdapter() {accountListAdapter = AccountListAdapter(this)accountListAdapter.setHasStableIds(true)account_recycler_view.adapter = accountListAdapteraccount_recycler_view.addItemDecoration(DividerItemDecoration(需要上下文()，DividerItemDecoration.VERTICAL))val accountTouchHelper = ItemTouchHelper(对象:ItemTouchHelper.SimpleCallback(ItemTouchHelper.UP 或 ItemTouchHelper.DOWN,0){覆盖乐趣 onSelectedChanged(viewHolder: RecyclerView.ViewHolder?,动作状态:Int){如果(actionState == ItemTouchHelper.ACTION_STATE_DRAG){val accountViewHolder = viewHolder 作为 AccountListAdapter.ViewHolderaccountViewHolder.onItemSelected()}super.onSelectedChanged(viewHolder, actionState)}覆盖有趣的 clearView(回收器视图:回收器视图，viewHolder: RecyclerView.ViewHolder){val accountViewHolder = viewHolder 作为 AccountListAdapter.ViewHolderaccountViewHolder.onItemClear()super.clearView(recyclerView, viewHolder)}覆盖乐趣 onMove(回收器视图:回收器视图，viewHolder: RecyclerView.ViewHolder,目标:RecyclerView.ViewHolder): 布尔 {val fromPos: Int = viewHolder.adapterPositionval toPos: Int = target.adapterPositionCollections.swap(_accountList, fromPos, toPos)accountListAdapter.notifyItemMoved(fromPos, toPos)返回真}覆盖乐趣 onSwiped(viewHolder: RecyclerView.ViewHolder, 方向: Int) {}})accountTouchHelper.attachToRecyclerView(accounts_recycler_view)}

解决方案

所以问题是我的 Recyclerview 在 ViewPager 里面，它在 ConstraintLayout.视图寻呼机被垂直约束，高度设置为 0dp，但宽度设置为 match_parent.我需要的只是将其水平约束，宽度设置为 0dp，setHasFixedSize = true 为 RecyclerView

当为适配器调用 notifyItemMoved 时，如果 RecyclerView 是灵活的，则所有项目都被重绘，默认情况下它会关注第一个项目.

I have this weird bug where my RecyclerView scrolls back to top position whenever I start dragging an item in it. It's inside ViewPager if that has any difference. You can see the behavior in .gif attached.

EDIT:

It seems that RecyclerView view scrolls to top when notifyItemMoved is called and it scrolls just as much for the first view to be at least partially displayed on screen.

View

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/accounts_recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:scrollbarStyle="outsideOverlay"
    android:scrollbars="none"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
    tools:listitem="@layout/view_account_list_item" />

Adapter

class AccountListAdapter(
private val onAccountClickListener: OnAccountClickListener) :
ListAdapter<Account, AccountListAdapter.ViewHolder>(
    AccountDiffCallback()
) {

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
    val inflater = LayoutInflater.from(parent.context)
    return ViewHolder(
        inflater.inflate(
            R.layout.view_account_list_item,
            parent,
            false
        )
    )
}

override fun getItemId(position: Int): Long {
    return getItem(position).accountId.toLong()
}

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    holder.bind(getItem(position), onAccountClickListener)
}

class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView), OnItemDragged {

    fun bind(account: Account, onAccountClickListener: OnAccountClickListener) {
        itemView.account_name.text = account.name
       
        itemView.setOnClickListener {
            onAccountClickListener.onAccountClick(account)
        }

    }

    override fun onItemSelected() {
        itemView.setBackgroundColor(
            ContextCompat.getColor(
                itemView.context,
                R.color.background_contrast
            )
        )
    }

    override fun onItemClear() {
        itemView.setBackgroundColor(
            ContextCompat.getColor(
                itemView.context,
                R.color.background
            )
        )
    }

}

class AccountDiffCallback : DiffUtil.ItemCallback<Account>() {
    override fun areItemsTheSame(oldItem: Account, newItem: Account): Boolean {
        return oldItem.accountId == newItem.accountId
    }

    override fun areContentsTheSame(oldItem: Account, newItem: Account): Boolean {
        return (oldItem.balance == newItem.balance
                && oldItem.annualReturn == newItem.annualReturn
                && oldItem.name == newItem.name)
    }
}

interface OnAccountClickListener {
    fun onAccountClick(account: Account)
}

interface OnItemDragged {
    fun onItemSelected()
    fun onItemClear()
}}

ItemTouchHelper

 private fun setupListAdapter() {

    accountListAdapter = AccountListAdapter(this)
    accountListAdapter.setHasStableIds(true)

    accounts_recycler_view.adapter = accountListAdapter
    accounts_recycler_view.addItemDecoration(
        DividerItemDecoration(
            requireContext(),
            DividerItemDecoration.VERTICAL
        )
    )


    val accountTouchHelper = ItemTouchHelper(
        object : ItemTouchHelper.SimpleCallback(
            ItemTouchHelper.UP or ItemTouchHelper.DOWN,
            0
        ) {

            override fun onSelectedChanged(
                viewHolder: RecyclerView.ViewHolder?,
                actionState: Int
            ) {
                if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) {
                    val accountViewHolder = viewHolder as AccountListAdapter.ViewHolder
                    accountViewHolder.onItemSelected()
                }
                super.onSelectedChanged(viewHolder, actionState)
            }

            override fun clearView(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder
            ) {
                val accountViewHolder = viewHolder as AccountListAdapter.ViewHolder
                accountViewHolder.onItemClear()
                super.clearView(recyclerView, viewHolder)
            }


            override fun onMove(
                recyclerView: RecyclerView,
                viewHolder: RecyclerView.ViewHolder,
                target: RecyclerView.ViewHolder
            ): Boolean {
                val fromPos: Int = viewHolder.adapterPosition
                val toPos: Int = target.adapterPosition
                Collections.swap(_accountList, fromPos, toPos)
                accountListAdapter.notifyItemMoved(fromPos, toPos)
                return true
            }

            override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {}

        })

    accountTouchHelper.attachToRecyclerView(accounts_recycler_view)

}

解决方案

So the issues was that my Recyclerview was inside ViewPager which was inside a ConstraintLayout . View pager was constrained vertically with height set to 0dp but width was set to match_parent. All I needed was to constrain it horizontally with width set to 0dp and setHasFixedSize = true to RecyclerView

When calling notifyItemMoved for adapter, if RecyclerView is flexible, all items are redrawn and by default it focuses on the first item.

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