Let’s scroll to the position of the posted item, which just created by a user, on the list using RecyclerView inside NestedScrollView.

Illustration by Ella Dobson

We often implement functionality such as commenting or posting using RecyclerView which has adapter is extended from ListAdapter inside a NestedScrollView. For example, a user writes a comment, sends it to a backend server and gets an updated list of comments within seconds. These may get rearranged according to the intent of the service or backend engineer. That is, it means we could receive the rearranged the list of items. How can we scroll to the correct position of list items a user just posted in RecyclerView inside NestedScrollView.

Let’s dive into it. :) Please refer to below code:

CommentReplyFragment : Function-Reply the comment

private fun postReply(info: CommentInfo, taggedUserId: String?) {
    val viewModel = PostCommentViewModel.provideFactory(
        postCommentViewModelFactory,Params(Query(......))
    ).create(PostCommentViewModel::class.java)

    view?.let {
        launchAndRepeatWithViewLifecycle {
            viewModel.value.collectLatest { resource ->
                when (resource.getStatus()) {
                    Status.SUCCESS -> {
                        resource.getData()?.let {
                            @Suppress("UNCHECKED_CAST")
                            val response = 
                                resource.getData() as? Response

                            ReplyAdapter?.let { adapter ->
                                lifecycleScope.launch {
                                    with(binding) {
                                        hideSendView(this, false)
                                        setCommentCount(++count)
                                    }
                                }

                                taggedNickname = ""
                                response?.let {
                                    it.payload.first { comment ->
                                        info.commentId == comment.id
                                    }?.children?.let { list ->
                                        replied = true
                                        adapter.isPosted = true
                                        adapter.reply =        
                                            detectInfo.comment                                        
                                        adapter.submitList(list)
                                        ...
                                    }
                                }
                            }
                        }
                    }

                    Status.ERROR -> {
                        showComment(binding, false)
                        showErrorPopup(resource.getMessage()!!) {}
                    }

                    Status.LOADING -> {
                        showComment(binding, true)
                    }
                }
            }
        }
    }
}

ReplyApdater : draw the received the items of list

class ReplyAdapter(
    private val replyFragment: CommentReplyFragment, ...
) : ListAdapter<Comment, ReplyAdapter.ItemHolder>(CommentDiffUtil) {
    private var _binding: ItemCommentBinding? = null
    private val binding get() = _binding!!

    internal var isPosted = false

    internal var reply = ""

    object CommentDiffUtil : DiffUtil.ItemCallback<Comment>() {
        override fun areItemsTheSame(
            oldItem: Comment, newItem: Comment): Boolean {
                return oldItem.id == newItem.id
            }
        )
override fun areContentsTheSame(
            oldItem: Comment, newItem: Comment
        ): Boolean {
            return oldItem.content == newItem.content
        }
    }

    override fun onCreateViewHolder(
        parent: ViewGroup, viewType: Int
    ): ItemHolder {
        val contextThemeWrapper =
            ContextThemeWrapper(
                replyFragment.homeActivity, R.style.AppTheme
            )

        _binding = null
        _binding = ItemCommentBinding.inflate(
            LayoutInflater.from(contextThemeWrapper),
            parent,
            false
        )

        return ItemHolder(binding)
    }

    @OptIn(ExperimentalTime::class)
    override fun onBindViewHolder(
        holder: ItemHolder, position: Int
    ) {
        val item = getItem(position)

        with(holder.binding) {
            ...
            ...

            tvComment.post {
                if (replyFragment.isAdded) {
                    with(replyFragment.binding) {
                        val params = rvReply.layoutParams

                        params.height = MATCH_PARENT
                        rvReply.layoutParams = params

                        if (isPosted && reply == item.content) {
                            vScroll.post {
                                rvReply.getChildAt(position)?.let {
                                    vScroll.scrollY = 
                                        (rvReply.y + it.y).toInt()
                                }
                            }

                            isPosted = false
                        }
                    }
                }
            }    
       
            ...
            ...
            
            containerReport.setSafeOnClickListener {
                replyFragment.lifecycleScope.launchWhenResumed {
                    showCommentReportDialog(
                        replyFragment.homeActivity,
                        item,
                        tvComment,
                        containerCommentCount,
                        likeContainer,
                        dislikeContainer,
                        containerReport
                    )
                }
            }
            ....
        }
    }

    override fun onViewDetachedFromWindow(holder: ItemHolder) {
        super.onViewDetachedFromWindow(holder)

        _binding = null
    }
    ....
    ....
    ....
}

CommentReplyAdapter.kt implemnted by Lukoh

Android Scroll Tech

Conclusion

This method would be very useful and easy for scrolling to the position of the posted item the user just created if the received list items may are rearranged.

Thank you so much for reading and I hope this article was helpful. If you have something to say to me, please leave a comment, and if this article was helpful, please share and clicks 👏.