Android Studio Kotlin SearchView, RecyclerView

activiti_main

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.google.android.material.appbar.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </com.google.android.material.appbar.AppBarLayout>

    <include layout="@layout/content_main" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

content_main

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context=".MainActivity"
    tools:showIn="@layout/activity_main">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</LinearLayout>

data_list_item

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="16dp">

    <TextView
        android:id="@+id/tv_item"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

res-menu menu_main

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item
        android:id="@+id/action_search"
        android:icon="@android:drawable/ic_menu_search"
        app:showAsAction="ifRoom"
        app:actionViewClass="androidx.appcompat.widget.SearchView"
        android:title="search"/>
</menu>

MainActivity.kt

class MainActivity : AppCompatActivity(), SearchView.OnQueryTextListener {

    private val dataList  = mutableListOf<String>()
    private val filteredList = mutableListOf<String>()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(toolbar)

        addData()
        recycler_view.layoutManager = LinearLayoutManager(this)
        recycler_view.adapter = DataAdapter(dataList)
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {

        menuInflater.inflate(R.menu.menu_main, menu)
        val searchView = menu.findItem(R.id.action_search).actionView as SearchView
        searchView.queryHint = getString(R.string.search_view_hint)
        searchView.setOnQueryTextListener(this)

        return super.onCreateOptionsMenu(menu)
    }


    override fun onQueryTextChange(entry: String): Boolean {

        filteredList.clear()

        (0 until dataList.size)
                .filter { dataList[it].toLowerCase().contains(entry.toLowerCase()) }
                .mapTo(filteredList) { dataList[it] }

        recycler_view.adapter = DataAdapter(filteredList)

        return true
    }

    override fun onQueryTextSubmit(query: String?): Boolean {
        return true
    }

    private fun addData() {

        dataList.add("100")
        dataList.add("200")
        dataList.add("300")
        dataList.add("400")
        dataList.add("500")
        dataList.add("600")
        dataList.add("700")
        dataList.add("800")

    }
}

DataAdapter

lass DataAdapter(private var items : MutableList<String>) :
        RecyclerView.Adapter<DataAdapter.ViewHolder>() {

    override fun getItemCount(): Int {
        return items.size
    }

    override fun onBindViewHolder(holder: ViewHolder, index: Int) {
        holder.item.text = items[index]
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        return ViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.data_list_item, parent, false))
    }

    class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        var item: TextView = itemView.tv_item
    }

build.gradle(app)

    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'com.google.android.material:material:1.0.0'
    implementation 'androidx.recyclerview:recyclerview:1.0.0'