kotlin 日付選択ダイアログ

DatePickerFragment.kt を作成し、MainActivity.kt で使用します。
日付を選択したらテキストビューに選択した日付を表示しています。

DatePickerFragment.kt


            package com.example.sampledatetimepickerdialog

import android.app.DatePickerDialog
import android.app.Dialog
import android.content.Context
import android.os.Bundle
import android.widget.DatePicker
import androidx.fragment.app.DialogFragment
import java.util.*

class DatePickerFragment: DialogFragment(), DatePickerDialog.OnDateSetListener {    // *1

    interface Listener {
        fun onDataSet(year: Int, month: Int, day: Int)
    }

    private lateinit var listener: Listener

    override fun onAttach(context: Context) {   // *2
        super.onAttach(context)
        when {
            parentFragment is Listener -> listener = parentFragment as Listener
            context is Listener -> listener = context
        }
    }

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        val c = Calendar.getInstance()
        val year = c.get(Calendar.YEAR)
        val month = c.get(Calendar.MONTH)
        val day = c.get(Calendar.DAY_OF_MONTH)

        return DatePickerDialog(requireActivity(), this, year, month, day)  // *3
    }

    override fun onDateSet(p0: DatePicker?, year: Int, month: Int, day: Int) {  // *4
        listener.onDataSet(year, month, day)
    }
}

MainActivity.kt


            package com.example.sampledatetimepickerdialog

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.example.sampledatetimepickerdialog.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity(), DatePickerFragment.Listener {    // *1
    private lateinit var binding: ActivityMainBinding
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        binding.btnDatePicker.setOnClickListener {  // *2
            val datePicker = DatePickerFragment()
            datePicker.show(supportFragmentManager, "Date picker dialog")
        }
    }

    override fun onDataSet(year: Int, month: Int, day: Int) {   // *3
        val m = (month + 1).toString().padStart(2, '0')
        val d = day.toString().padStart(2, '0')
        val str = "$year-$m-$d"
        binding.txvSample.text = str
    }

}