Fragment takes time to load RecyclerView when the list is large

Question

I have a RecyclerView implemented along with Paging to load a list from Room Database. The list works fine when the size is small. When the size reaches around 50 - 60, the list still works fine but when i switch to another fragment and then come back to the list, its blocks the UI for around 1.5 - 2 seconds which is super dull in user experience (See GIF below):

My code is as follows:

DAO

@Query("SELECT * FROM account_table WHERE userID = :userID")
fun getAll(userID: String): DataSource.Factory

Repository

class AccountRepository private constructor(application: Application) {

private val database =
    LockyDatabase.getDatabase(
        application
    )
private val accountDao = database.accountDao()

companion object {
    @Volatile
    private var instance: AccountRepository? = null

    fun getInstance(application: Application) =
        instance ?: synchronized(this) {
            instance ?: AccountRepository(application).also { instance = it }
        }
}

fun getAll(userID: String) = accountDao.getAll(userID)

}

adapter

class CredentialsPagingAdapter(
private val clickListener: ClickListener,
private val optionsClickListener: OptionsClickListener?,
private val isSimplified: Boolean
) : PagedListAdapter(
    diffCallback
) {
    companion object {
        private val diffCallback = object : DiffUtil.ItemCallback() {
            override fun areItemsTheSame(oldItem: Credentials, newItem: Credentials): Boolean {
                return oldItem.id == newItem.id
            }

        override fun areContentsTheSame(oldItem: Credentials, newItem: Credentials): Boolean {
            return oldItem.equals(newItem)
        }
    }
}

override fun onBindViewHolder(holder: CredentialsViewHolder, position: Int) {
    holder.bind(
        clickListener,
        optionsClickListener,
        getItem(position),
        isSimplified
    )
}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CredentialsViewHolder {
    return CredentialsViewHolder.from(
        parent
    )
}
}

viewModel

val accounts = Transformations.switchMap(_sort) {
    when (true) {
        it.name -> _accounts.sortByEntryName
        it.username -> _accounts.sortByUsername
        it.email -> _accounts.sortByEmail
        it.website -> _accounts.sortByWebsite
        it.authType -> _accounts.sortByAuthenticationType
        else -> _accounts
    }.toLiveData(pageSize = resources.getInteger(R.integer.size_paging_list_default))
}

fragment

private fun subscribeAccounts() {
    val adapter = CredentialsPagingAdapter(
        /* The click listener to handle account on clicks */
        ClickListener {
            navigateTo(
                AccountFragmentDirections.actionFragmentAccountToFragmentViewAccount(
                    it as Account
                )
            )
        },
        /* The click listener to handle popup menu for each accounts */
        OptionsClickListener { view, credential ->
            view.apply {
                isEnabled = false
            }
            createPopupMenu(view, credential as Account)
        },
        false
    )

    binding.RecyclerViewAccount.apply {
        /*
        * State that layout size will not change for better performance
        */
        setHasFixedSize(true)

        /* Bind the layout manager */
        layoutManager = LinearLayoutManager(requireContext())

        /* Bind the adapter */
        this.adapter = adapter
    }

    viewModel.accounts.observe(viewLifecycleOwner, Observer {
        if (it != null) {
            /*
             * If accounts is not null
             * Load recyclerview and
             * Update the ui
             */
            lifecycleScope.launch {
                adapter.submitList(it as PagedList)
            }

            updateUI(it.size)
        }
    })
}

Main Activity Layout

...

Fragment Account Layout:

Recyclerview List Layout

My paging version is 2.1.2

Can someone please help me on this. I tried several days looking for fix but nothing works.

I appreciate the help.

ianhanniballake · Accepted Answer

You must remove your NestedScrollView (Nested_Scroll) in your activity layout - you cannot put a vertical RecyclerView within a NestedScrollView.

A NestedScrollView expands every child in the vertical scroll direction to determine the maximum scroll distance. This means that it gives the RecyclerView an infinite height to expand into. This causes RecyclerView to inflate every element, defeating all view recycling and defeating the use of paging - given infinite height, it'll continue to ask Paging for more and more rows to fill the space.

Fragment takes time to load RecyclerView when the list is large

Answers (1)

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