android kotlin - List filter not null example

MainActivity.kt

package com.cfsuman.kotlintutorials

import android.os.Bundle
import android.text.method.ScrollingMovementMethod
import android.widget.Button
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity


class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // get the widgets reference from XML layout
        val textView = findViewById<TextView>(R.id.textView)
        val btnList = findViewById<Button>(R.id.btnList)
        val btnFilterNotNull = findViewById<Button>(
            R.id.btnFilterNotNull)
        val btnFilterNotNullTo = findViewById<Button>(
            R.id.btnFilterNotNullTo)


        // make textview content scrollable
        textView.movementMethod = ScrollingMovementMethod()


        val list = listOf("Red",null,"Green",
            "Yellow",null,"Black","White",null)


        btnList.setOnClickListener {
            textView.text = "List:\n"

            // Iterate through the list
            list.forEach {
                textView.append("\n$it")
            }
        }


        btnFilterNotNull.setOnClickListener {
            // Filter nulls value from the list
            // and generate new list
            val filtered = list.filterNotNull()

            textView.text = "Filtered list without null values\n"
            // Iterate through the filtered list
            filtered.forEach {
                textView.append("\n$it")
            }
        }


        btnFilterNotNullTo.setOnClickListener {
            val favColors = mutableListOf("Pink","Olive")

            textView.text = "Favorite colors\n"
            // Iterate through the filtered list
            favColors.forEach {
                textView.append("\n$it")
            }

            // Copy the not null values from the
            // list to favorite colors list
            list.filterNotNullTo(favColors)

            textView.append("\n\nFav colors with another" +
                    " list's non null values\n")
            // Iterate through the filtered list
            favColors.forEach {
                textView.append("\n$it")
            }
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#F8F8F8"
    android:padding="24dp">

    <Button
        android:id="@+id/btnList"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="List"
        android:textAllCaps="false"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btnFilterNotNull"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="filterNotnull"
        android:textAllCaps="false"
        app:layout_constraintBottom_toBottomOf="@+id/btnList"
        app:layout_constraintStart_toEndOf="@+id/btnList" />

    <Button
        android:id="@+id/btnFilterNotNullTo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="filterNotNullT0"
        android:textAllCaps="false"
        app:layout_constraintBottom_toBottomOf="@+id/btnFilterNotNull"
        app:layout_constraintStart_toEndOf="@+id/btnFilterNotNull" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginTop="16dp"
        android:fontFamily="sans-serif"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btnList" />

</androidx.constraintlayout.widget.ConstraintLayout>