DatePickerFragment.kt

class DatePickerFragment : DialogFragment(), DatePickerDialog.OnDateSetListener {

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        // Use the current date as the default date in the picker
        val c = Calendar.getInstance()
        val year = c.get(Calendar.YEAR)
        val month = c.get(Calendar.MONTH)
        val day = c.get(Calendar.DAY_OF_MONTH)

        // Create a new instance of DatePickerDialog and return it
        return DatePickerDialog(activity!!, this, year, month, day)
    }

    override fun onDateSet(view: DatePicker, year: Int, month: Int, day: Int) {
        // Do something with the date chosen by the user
        val date_picked = "".plus(day).plus("/").plus(month).plus("/").plus(year)
        (activity as MyActivity).updateDate(date_picked)
    }
}