DatePickerDialogの年月を使ってソートしたい

家計簿アプリを作成しています。家計簿アプリでは月ごとの収支を一覧表示させたいと考えています。家計簿の収支データはもちろん2018年の11月のデータもあれば2018年の12月のデータも格納されていると仮定します。DatePickerDialogで年月を選択し(2018/12と選択したとします)、OKと押したときに2018/12で曖昧検索をし、2018年の12月のデータのみ一覧表示させたいと考えています。DatePickerDialogを使って検索値となる2018/12のデータは取ってこれるのですが、DatePickerDialogの処理を書く場所と書き方がよくわからず困っています。
どなたかご教授お願いします。

package com.example.username.kakeibo


import android.content.Intent
import android.os.Bundle
import android.support.design.internal.BottomNavigationItemView
import android.support.v4.app.Fragment
import android.support.v4.app.FragmentActivity
import android.view.View
import android.widget.Button
import android.widget.ImageButton
import android.widget.ListView
import android.widget.TextView
import io.realm.Realm
import io.realm.RealmConfiguration
import io.realm.RealmResults
import io.realm.kotlin.where
import kotlinx.android.synthetic.main.activity_kakeibo.*
import kotlinx.android.synthetic.main.kakeibolist.*
import java.util.*


class kakeiboActivity : FragmentActivity(), DatePick.Callback {
    private lateinit var realm: Realm
    private fun initRealm() {
        val realmConfiguration = RealmConfiguration.Builder()
            .deleteRealmIfMigrationNeeded()
            .schemaVersion(0)
            .build()
        realm = Realm.getInstance(realmConfiguration)

    }

    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_kakeibo)

        val config = RealmConfiguration.Builder().deleteRealmIfMigrationNeeded().build()
        val test_navi = findViewById<Button>(R.id.insert_button)
        val reload = findViewById<ImageButton>(R.id.reload_button)

        Realm.setDefaultConfiguration(config)

        realm = Realm.getDefaultInstance()


        var listView: ListView


        insert_button.setOnClickListener {
            val intent = Intent(application, Kakeibo_AddActivity::class.java)
            startActivity(intent)
        }
        val kakeibo_navi: BottomNavigationItemView = findViewById(R.id.navigation_kakeibo)
        val resito_navi: BottomNavigationItemView = findViewById(R.id.navigation_resito)
        val buylist_navi: BottomNavigationItemView = findViewById(R.id.navigation_buylist)
        val recipe_navi: BottomNavigationItemView = findViewById(R.id.navigation_recipe)
        kakeibo_navi.setOnClickListener {
            val intent = Intent(this, kakeiboActivity::class.java)
            startActivity(intent)
        }
        buylist_navi.setOnClickListener {
            val intent = Intent(this, buylistActivity::class.java)
            startActivity(intent)
        }
        resito_navi.setOnClickListener {
            val intent = Intent(this, resitoActivity::class.java)

            startActivity(intent)
        }
        recipe_navi.setOnClickListener {
            val intent = Intent(this, MainActivity::class.java)
            startActivity(intent)
        }

        listView = findViewById(R.id.kakeibolist)

        val Kakeibo = realm.where<Kakeibo>().findAll()
        listView?.adapter = KakeiboAdapter(Kakeibo)



    }
    override fun onDestroy() {
        super.onDestroy()
        realm.close()
    }
    override fun onDatePicked(year: Int,monthOfYear: Int, dayOfMonth: Int)  {
        val str = String.format(Locale.US, "%d/%d", year, monthOfYear+1 , dayOfMonth)
        calendar.text = str
    }
    override fun onAttachFragment(fragment : Fragment)  {
        if(fragment is DatePick)   {
            fragment.callback = this
        }
    }
    fun showDatePickerDialog(view: View) {
        val newFragment = DatePick()
        newFragment.show(supportFragmentManager, "datePicker")
        }

}

package com.example.username.kakeibo

import android.app.DatePickerDialog
import android.app.Dialog
import android.os.Bundle
import android.support.v4.app.DialogFragment
import android.widget.DatePicker
import java.util.*

class DatePick : DialogFragment(),DatePickerDialog.OnDateSetListener {
    var callback : Callback? = null

    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(activity,this, year,month,day)
    }
    override fun onDateSet(view: DatePicker, year: Int,month: Int, dayOfMonth: Int) {
        callback?.onDatePicked(year , month , dayOfMonth)
    }
    interface Callback  {
        fun onDatePicked(year : Int , monthOfYear: Int , dayOfMonth: Int)
    }
}

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

    <TextView
            android:id="@+id/calendar"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="16dp"
            android:text="@string/title_nengetu"
            android:textSize="25dp"
            android:onClick="showDatePickerDialog1"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            android:layout_marginTop="12dp"
    />

    <View
            android:layout_width="match_parent"
            android:layout_height="2.5dp"
            android:background="@color/blackColor"
            android:layout_marginLeft="10dp"
            android:layout_marginRight="10dp"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintHorizontal_bias="1.0"
            app:layout_constraintVertical_bias="0.092"/>

    <android.support.design.widget.BottomNavigationView
            android:id="@+id/navigation"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginEnd="0dp"
            android:layout_marginStart="0dp"
            android:background="?android:attr/windowBackground"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:menu="@menu/navigation"/>
    <ListView
            android:id="@+id/kakeibolist"
            android:layout_width="382dp"
            android:layout_height="405dp"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintVertical_bias="0.433"/>
    <Button
            android:id="@+id/insert_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/insert_gamen"
            android:layout_marginBottom="300dp"
            android:layout_marginLeft="260dp"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintHorizontal_bias="0.0" app:layout_constraintVertical_bias="0.0"/>
</android.support.constraint.ConstraintLayout>