How to use search functionality in custom listview in Android using kotlin?

This example demonstrates how to use search functionality in custom listview in Android using kotlin
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:padding="4dp"
   tools:context=".MainActivity">
   <EditText
      android:id="@+id/etSearch"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:hint="Search here" />
   <ListView
      android:id="@+id/listView"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:layout_below="@id/etSearch" />
</RelativeLayout>
Step 3 − Add the following code to src/MainActivity.kt
import android.os.Bundle
import android.text.Editable
import android.text.TextWatcher
import android.widget.ArrayAdapter
import android.widget.EditText
import android.widget.ListView
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
   lateinit var listView: ListView
   var months: ArrayList<String> = ArrayList()
   var arrayAdapter: ArrayAdapter<String>? = null
   lateinit var etSearch: EditText
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      title = "KotlinApp"
      listView = findViewById(R.id.listView)
      etSearch = findViewById(R.id.etSearch)
      months.add("January")
      months.add("February")
      months.add("March")
      months.add("April")
      months.add("May")
      months.add("June")
      months.add("July")
      months.add("August")
      months.add("September")
      months.add("October")
      months.add("November")
      months.add("December")
      arrayAdapter = ArrayAdapter(this, android.R.layout.simple_list_item_1, android.R.id.text1, months)
      listView.adapter = arrayAdapter
      etSearch.addTextChangedListener(object : TextWatcher {
         override fun beforeTextChanged(s: CharSequence, start: Int, count: Int, after: Int) {}
         override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {
            arrayAdapter!!.filter.filter(s)
         }
         override fun afterTextChanged(s: Editable) {}
      })
   }
}
Step 4 − Add the following code to androidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.q11">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click the Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen.