Gist to showcase expanding/collpasing items

MainListAdapter.kt

override fun onBindViewHolder(holder: ListViewHolder, position: Int) {
    val model = adapterList[position]

    // set expand state on binded items because views are recycler
    expandItem(holder, model == expandedModel, animate = false)

    holder.cardContainer.setOnClickListener {
        if (expandedModel == null) {
            // expand clicked view
            expandItem(holder, expand = true, animate = true)
            expandedModel = model
        } else if (expandedModel == model) {
            // collapse clicked view
            expandItem(holder, expand = false, animate = true)
            expandedModel = null
        } else {
            // collapse previously expanded view
            val expandedModelPosition = adapterList.indexOf(expandedModel!!)
            val oldViewHolder =
                    recyclerView.findViewHolderForAdapterPosition(expandedModelPosition) as? ListViewHolder
            if (oldViewHolder != null) expandItem(oldViewHolder, expand = false, animate = true)

            // expand clicked view
            expandItem(holder, expand = true, animate = true)
            expandedModel = model
        }
    }
}