How to Create Dialog Series Datepicker - Kotlin

MyDialogFragment.kt

class MyDialogFragment : DialogFragment(), DatePickerDialog.OnDateSetListener {

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {

        val dialog = activity?.let {
            // デフォルトの日付を用意
            val c = Calendar.getInstance()
            val year = c[Calendar.YEAR]
            val month = c[Calendar.MONTH]
            val day = c[Calendar.DAY_OF_MONTH]

            DatePickerDialog(it, this, year, month, day)
        }
        return dialog ?: throw IllegalStateException("アクティビティがNullです。")
    }

    override fun onDateSet(view: DatePicker, year: Int, month: Int, dayOfMonth: Int) {
        val msg = "${year}年${(month+1)}月${dayOfMonth}日"
        Toast.makeText(context, msg, Toast.LENGTH_SHORT).show()
    }
}