"Creating a RecyclerView with multiple content types and layouts in Kotlin" @ https://blog.jakelee.co.uk/creating-a-recyclerview-with-multiple-content-types-and-layouts-in-kotlin

activity_main.xml

    <android.support.v7.widget.RecyclerView
            android:id="@+id/recyclerView"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

ContentAdapter.kt

class ContentAdapter(private val rows: List<IRow>) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    interface IRow
    class HeaderRow(val date: String, val title: String) : IRow
    class MessageRow(val message: String) : IRow
    class ColourRow(val colour: Int) : IRow

    class HeaderViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val dateView: TextView = itemView.findViewById(R.id.date)
        val titleView: TextView = itemView.findViewById(R.id.title)
    }

    class MessageViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val messageView: TextView = itemView.findViewById(R.id.message)
    }

    class ColourViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val colourView: ImageView = itemView.findViewById(R.id.colour)
    }

    override fun getItemCount() = rows.count()

    override fun getItemViewType(position: Int): Int =
        when (rows[position]) {
            is HeaderRow -> TYPE_HEADER
            is MessageRow -> TYPE_MESSAGE
            is ColourRow -> TYPE_COLOUR
            else -> throw IllegalArgumentException()
        }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) = when (viewType) {
            TYPE_HEADER -> HeaderViewHolder(LayoutInflater.from(parent.context)
                .inflate(R.layout.row_header, parent, false))
            TYPE_MESSAGE -> MessageViewHolder(LayoutInflater.from(parent.context)
                .inflate(R.layout.row_message, parent, false))
            TYPE_COLOUR -> ColourViewHolder(LayoutInflater.from(parent.context)
                .inflate(R.layout.row_colour, parent, false))
            else -> throw IllegalArgumentException()
        }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) =
        when (holder.itemViewType) {
            TYPE_HEADER -> onBindHeader(holder, rows[position] as ContentAdapter.HeaderRow)
            TYPE_MESSAGE -> onBindMessage(holder, rows[position] as ContentAdapter.MessageRow)
            TYPE_COLOUR -> onBindColour(holder, rows[position] as ContentAdapter.ColourRow)
            else -> throw IllegalArgumentException()
        }

    private fun onBindHeader(holder: RecyclerView.ViewHolder, row: HeaderRow) {
        val headerRow = holder as HeaderViewHolder
        headerRow.titleView.text = row.title
        headerRow.dateView.text = row.date
    }

    private fun onBindMessage(holder: RecyclerView.ViewHolder, row: MessageRow) {
        (holder as MessageViewHolder).messageView.text = row.message
    }

    private fun onBindColour(holder: RecyclerView.ViewHolder, row: ColourRow) {
        (holder as ColourViewHolder).colourView.setBackgroundColor(row.colour)
    }

    companion object {
        private const val TYPE_HEADER = 0
        private const val TYPE_MESSAGE = 1
        private const val TYPE_COLOUR = 2
    }
}

MainActivity.kt

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        recyclerView.adapter = ContentAdapter(getSampleRows(10))
        recyclerView.layoutManager = LinearLayoutManager(this)
    }

    private fun getSampleRows(numSections: Int): List<ContentAdapter.IRow> {
        val rows = mutableListOf<ContentAdapter.IRow>()
        for (i in 1..numSections) {
            rows.add(ContentAdapter.HeaderRow(Randomiser.date(), Randomiser.word()))
            val numChildren = Randomiser.int(0, 10)
            for (j in 1..numChildren) {
                if(Randomiser.int(0, 1) > 0) {
                    rows.add(ContentAdapter.MessageRow(Randomiser.message()))
                } else {
                    rows.add(ContentAdapter.ColourRow(Randomiser.colour()))
                }
            }
        }
        return rows
    }
}

Randomiser.kt

class Randomiser {
    companion object {
        fun int(min: Int, max: Int): Int {
            return (min..max).shuffled().last()
        }

        fun date(): String {
            val calendar = Calendar.getInstance()
            calendar.add(Calendar.DAY_OF_YEAR, -int(0, 1000))
            val format = SimpleDateFormat("dd/MM/yyyy", Locale.UK)
            return format.format(calendar.time)
        }

        fun word() = ('a'..'z').map { it }.shuffled().subList(0, 8).joinToString("").capitalize()

        fun message() = UUID.randomUUID().toString()

        fun colour(): Int {
            val rnd = Random()
            return Color.argb(255, rnd.nextInt(256), rnd.nextInt(256), rnd.nextInt(256))
        }
    }
}

row_colour.xml

<ImageView
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/colour"
        android:layout_height="50dp"
        android:layout_width="match_parent" />

row_header.xml

<android.support.constraint.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@android:color/black">
    <TextView
            android:id="@+id/title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            android:paddingStart="10dp"
            android:textColor="@android:color/white"
            android:textSize="18sp"/>
    <TextView
            android:id="@+id/date"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toEndOf="@id/title"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintHorizontal_bias="1.0"
            android:paddingEnd="10dp"
            android:textColor="@android:color/white"
            android:textSize="18sp"/>
</android.support.constraint.ConstraintLayout>

row_message.xml

<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="10dp">
    <TextView
            android:id="@+id/message"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
</android.support.constraint.ConstraintLayout>