Reddit code review request

ViewPager.kt

enum class PAGE_TYPES {color, manufacturer}
const val noFilter = "no filter"

class ViewPagerAdapter(private val context: Context?, private val viewModel: SharedViewModel): RecyclerView.Adapter<ViewPagerAdapter.VPAViewHolder>() {
    private val data = HashMap<String, List<String>>()

    class VPAViewHolder(view: View?): RecyclerView.ViewHolder(view!!) {
        val radioGroup:RadioGroup = view!!.findViewById<RadioGroup>(R.id.options)
        val title: TextView = view!!.findViewById<TextView>(R.id.title)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VPAViewHolder {
        var view = LayoutInflater.from(context).inflate(R.layout.pager_adapter_item, parent, false)
        return VPAViewHolder(view)
    }

    override fun onBindViewHolder(holder: VPAViewHolder, position: Int) {
        // which page are we on
        val key = when(position) {
            0 -> PAGE_TYPES.color.toString()
            else -> PAGE_TYPES.manufacturer.toString()
        }

        // we are going to generate a radio group, get the right list of options.
        val options = data[key] ?: listOf<String>()

        // Set title to right message, or loading if options haven't been stocked yet
        val title = if (options.isEmpty()) {
            context?.resources?.getString(R.string.loading) ?: ""
        } else {
            context?.resources?.getString(R.string.filter, key) ?: ""
        }
        holder.title.setText(title)

        // build the radio buttons
        holder.radioGroup.removeAllViews()
        options.forEachIndexed(){i, option ->
            val radioButton = RadioButton(context)
            radioButton.text = option
            radioButton.id = i
            if (key == PAGE_TYPES.manufacturer.toString() && viewModel.manufacturerFilter == option) {
                radioButton.isChecked = true
            }
            if (key == PAGE_TYPES.color.toString() && viewModel.colorFilter == option) {
                radioButton.isChecked = true
            }
            holder.radioGroup.addView(radioButton)
        }

        // bind the right check changed listener to update the view model on check.
        if (key == PAGE_TYPES.manufacturer.toString()) {
            holder.radioGroup.setOnCheckedChangeListener{
                    _, id ->
                    val option = options[id]
                    viewModel.manufacturerFilter = option
            }
        } else {
            holder.radioGroup.setOnCheckedChangeListener{
                    _, id ->
                val option = options[id]
                viewModel.colorFilter = option
            }
        }

    }

    override fun getItemCount(): Int = 2

    fun addData(key: String, options: List<String>) {
        val augmentedList = options + noFilter
        data[key] = augmentedList
        notifyDataSetChanged()
    }

}