How to implement sticky headers in a RecyclerView in Kotlin Android

How to implement sticky headers in a RecyclerView in Kotlin Android.

Here's a step-by-step tutorial on how to implement sticky headers in a RecyclerView in Kotlin Android.

Step 1: Set up the RecyclerView

First, make sure you have a RecyclerView set up in your activity or fragment layout file. You can do this by adding the following code to your XML layout file:

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

Step 2: Create the Adapter

Next, create an adapter class for your RecyclerView. This adapter will be responsible for binding data to the views in your list. It will also handle the logic for displaying sticky headers.

Here's an example of how you can create the adapter class:

class MyAdapter(private val items: List<Item>) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    // View types
    private val ITEM = 0
    private val HEADER = 1

    // ViewHolders
    inner class ItemViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        // Bind item data to views
        fun bind(item: Item) {
            // Bind item data to views
        }
    }

    inner class HeaderViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        // Bind header data to views
        fun bind(header: String) {
            // Bind header data to views
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        val inflater = LayoutInflater.from(parent.context)
        return when (viewType) {
            ITEM -> {
                val itemView = inflater.inflate(R.layout.item_layout, parent, false)
                ItemViewHolder(itemView)
            }
            HEADER -> {
                val headerView = inflater.inflate(R.layout.header_layout, parent, false)
                HeaderViewHolder(headerView)
            }
            else -> throw IllegalArgumentException("Invalid view type")
        }
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        val item = items[position]
        when (holder) {
            is ItemViewHolder -> holder.bind(item)
            is HeaderViewHolder -> holder.bind(item.header)
        }
    }

    override fun getItemCount(): Int {
        return items.size
    }

    override fun getItemViewType(position: Int): Int {
        return if (items[position].isHeader) HEADER else ITEM
    }
}

Step 3: Add Sticky Headers

To add sticky headers to your RecyclerView, you'll need to modify your adapter class and implement a few additional methods.

First, you'll need to add a method to determine whether a specific item is a header or not:

override fun getItemViewType(position: Int): Int {
    return if (items[position].isHeader) HEADER else ITEM
}

Next, you'll need to add logic to handle the sticky behavior in your onBindViewHolder method. You can use a combination of getItemViewType and getAdapterPosition to determine if the current item is a header or not, and if it should be sticky:

override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
    val item = items[position]
    val viewType = getItemViewType(position)

    if (viewType == HEADER && position > 0) {
        val prevItem = items[position - 1]
        if (prevItem.isHeader) {
            // Calculate the sticky behavior
            if (item.header != prevItem.header) {
                holder.itemView.visibility = View.VISIBLE
            } else {
                holder.itemView.visibility = View.GONE
            }
        } else {
            holder.itemView.visibility = View.VISIBLE
        }
    } else {
        holder.itemView.visibility = View.VISIBLE
    }

    when (holder) {
        is ItemViewHolder -> holder.bind(item)
        is HeaderViewHolder -> holder.bind(item.header)
    }
}

Finally, you'll need to update your XML layout files for the item and header views to include any additional styling or layout you want for your sticky headers.

That's it! You've successfully implemented sticky headers in a RecyclerView in Kotlin Android. Now you can run your app and see the sticky headers in action.