Sticky Header with Click Listeners for Recycler View

HomeFragment.kt

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.recyclerview.widget.LinearLayoutManager
import com.example.stickyheader.databinding.FragmentHomeListBinding
import com.example.stickyheader.header.StickyHeaderItemDecorator
import com.example.stickyheader.model.ItemModel


class HomeFragment : Fragment() {

    private var _binding: FragmentHomeListBinding? = null
    private val binding get() = _binding
    private var stickyHeaderItemDecorator: StickyHeaderItemDecorator? = null

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    ): View? {
        _binding = FragmentHomeListBinding.inflate(inflater, container, false)
        return binding?.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        initAdapter()
        initStickyItemDecorator()
    }

    private fun initStickyItemDecorator() {
        stickyHeaderItemDecorator?.clearReferences()
        stickyHeaderItemDecorator = null

        stickyHeaderItemDecorator = StickyHeaderItemDecorator()
        binding?.recyclerList?.let {
            val adapter = it.adapter
            if (adapter is ListRecyclerAdapter) {
                stickyHeaderItemDecorator?.attachRecyclerView(
                    adapter,
                    it,
                    adapter
                )
            }
        }
    }

    private fun initAdapter() {
        binding?.recyclerList?.apply {
            layoutManager = LinearLayoutManager(context)
            adapter = ListRecyclerAdapter(getDummyItems()) {
                (activity as? MainActivity)?.launchDetailPage(it)
            }
        }
    }

    private fun getDummyItems(): List<ItemModel> {
        return arrayListOf(
            ItemModel(),
            ItemModel(),
            ItemModel(isHeader = true),
            ItemModel(),
            ItemModel(),
            ItemModel(),
            ItemModel(),
            ItemModel(isHeader = true),
            ItemModel(),
            ItemModel(),
            ItemModel(),
            ItemModel(isHeader = true),
            ItemModel(),
            ItemModel(),
            ItemModel(),
            ItemModel(),
            ItemModel(),
            ItemModel()
        )
    }

    companion object {

        @JvmStatic
        fun newInstance() = HomeFragment()
    }
}

ids.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <item name="sticky_header_container" type="id"/>
</resources>

ListRecyclerAdapter.kt

class ListRecyclerAdapter(
    private val itemsList: List<ItemModel>,
    private val onHeaderItemClick: (Int) -> Unit
) : RecyclerView.Adapter<RecyclerView.ViewHolder>(),
    StickyHeaderItemDecorator.StickyHeaderInterface {

    companion object {
        const val TYPE_HEADER = 1
        const val TYPE_CONTENT = 2
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {

        return when (viewType) {
            TYPE_HEADER -> HeaderViewHolder(
                ItemHeaderBinding.inflate(
                    LayoutInflater.from(parent.context),
                    parent,
                    false
                )
            )

            else -> ItemBodyViewHolder(
                ItemListBinding.inflate(
                    LayoutInflater.from(parent.context),
                    parent,
                    false
                )
            )
        }
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        when (holder) {
            is HeaderViewHolder -> {
                holder.contentView.text = "Header $position"
                holder.nextButton.setOnClickListener { onHeaderItemClick(position) }
            }

            is ItemBodyViewHolder -> holder.contentView.text = "Content body at position $position"
        }
    }

    override fun getItemCount(): Int = itemsList.size

    override fun getItemViewType(position: Int) =
        if (itemsList[position].isHeader) TYPE_HEADER else TYPE_CONTENT

    inner class ItemBodyViewHolder(binding: ItemListBinding) :
        RecyclerView.ViewHolder(binding.root) {
        val contentView: TextView = binding.content
    }

    inner class HeaderViewHolder(binding: ItemHeaderBinding) :
        RecyclerView.ViewHolder(binding.root) {
        val contentView: TextView = binding.content
        val nextButton: TextView = binding.nextText
    }

    override fun isHeader(itemPosition: Int) = itemsList[itemPosition].isHeader

}

StickyHeaderItemDecorator.kt

import android.view.View
import android.view.ViewGroup
import android.widget.LinearLayout
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.stickyheader.ListRecyclerAdapter
import com.example.stickyheader.R

class StickyHeaderItemDecorator {

    private lateinit var listener: StickyHeaderInterface
    private lateinit var recyclerView: RecyclerView
    private lateinit var adapter: ListRecyclerAdapter
    private val currentHeaderViewMap: MutableMap<Int, Boolean> by lazy { mutableMapOf() }
    private var stickyHeaderContainer: LinearLayout? = null

    fun attachRecyclerView(
        listener: StickyHeaderInterface,
        recyclerView: RecyclerView,
        adapter: ListRecyclerAdapter
    ) {
        this.listener = listener
        this.recyclerView = recyclerView
        this.adapter = adapter
        initContainer()
        clearHeaderViews()
        refreshHeader()
    }

    private fun initContainer() {
        stickyHeaderContainer =
            (recyclerView.parent as? ViewGroup)?.findViewById(R.id.sticky_header_container)
        if (stickyHeaderContainer == null) {
            // RecyclerViews parent should be FrameLayout or RelativeLayout to add sticky header at top
            val linearLayout = LinearLayout(recyclerView.context)
            stickyHeaderContainer = linearLayout
            val params = ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.WRAP_CONTENT
            )
            stickyHeaderContainer?.id = R.id.sticky_header_container
            stickyHeaderContainer?.orientation = LinearLayout.VERTICAL
            (recyclerView.parent as? ViewGroup)?.addView(stickyHeaderContainer, params)
        }
        recyclerView.addOnScrollListener(onScrollChangeListener)
    }

    private fun clearHeaderViews() {
        currentHeaderViewMap.clear()
        stickyHeaderContainer?.removeAllViews()
    }

    private fun addHeaderViewFromPosition(position: Int) {
        if (currentHeaderViewMap[position] == true) return // return if header already added

        stickyHeaderContainer?.let {
            val vh = adapter.createViewHolder(it, adapter.getItemViewType(position))
            adapter.bindViewHolder(vh, position)
            val view = vh.itemView
            view.tag = position
            it.addView(
                view,
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.WRAP_CONTENT
            )
            currentHeaderViewMap[position] = true
            recyclerView.post { it.requestLayout() }
        }
    }

    private fun removeHeaderViewFromPosition(position: Int) {
        if (currentHeaderViewMap[position] != true) return // already removed

        val view = stickyHeaderContainer?.findViewWithTag<View>(position)
        view?.let {
            stickyHeaderContainer?.removeView(it)
        }
        currentHeaderViewMap[position] = false
    }

    private fun drawHeaders() {
        val layoutManager = recyclerView.layoutManager as? LinearLayoutManager?
        var topChildPosition = layoutManager?.findFirstVisibleItemPosition() ?: 0
        var i = 0
        while (i <= topChildPosition) {
            if (i == RecyclerView.NO_POSITION) break
            if (listener.isHeader(i)) {
                removeExistingHeaders(i) // Can be removed if needed stacked type sticky headers
                addHeaderViewFromPosition(i)
                topChildPosition++
            }
            i++
        }
    }

    private fun removeExistingHeaders(i: Int) {
        currentHeaderViewMap.forEach { (key, value) ->
            if ((!listener.isHeader(key) || key < i) && value) {
                removeHeaderViewFromPosition(key)
            }
        }
    }

    private fun removeInvalidHeaders() {
        val layoutManager = recyclerView.layoutManager as? LinearLayoutManager?
        val topChildPosition =
            layoutManager?.findFirstVisibleItemPosition() ?: 0
        currentHeaderViewMap.forEach { (key, value) ->
            if ((!listener.isHeader(key) || key > topChildPosition) && value) {
                removeHeaderViewFromPosition(key)
            }
        }
    }

    private val onScrollChangeListener: RecyclerView.OnScrollListener =
        object : RecyclerView.OnScrollListener() {
            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                super.onScrolled(recyclerView, dx, dy)
                refreshHeader()
            }
        }

    fun refreshHeader() {
        recyclerView.post {
            removeInvalidHeaders()
            drawHeaders()
        }
    }

    fun clearReferences() {
        recyclerView.removeOnScrollListener(onScrollChangeListener)
    }

    interface StickyHeaderInterface {
        fun isHeader(itemPosition: Int): Boolean
    }
}