android kotlin - removeAll and retainAll 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 btnRemoveAll = findViewById<Button>(R.id.btnRemoveAll)
        val btnRetainAll = findViewById<Button>(R.id.btnRetainAll)

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


        btnList.setOnClickListener {
            // Create a list with values
            val list = mutableListOf("RED","GREEN","BLACK",
                "YELLOW","WHITE","BLUE")
            textView.text = "Colors:\n"

            // Iterate through the list
            list.forEachIndexed { index, color ->
                textView.append("\n${index+1}. $color")
            }
        }


        btnRemoveAll.setOnClickListener {
            // Create a list with values
            val list = mutableListOf("RED","GREEN","BLACK",
                "YELLOW","WHITE","BLUE")

            // Remove elements which name stars with 'B'
            list.removeAll{ it.startsWith("B") }

            textView.text = "Remove all colors," +
                    " name starts with 'B'\n"

            // Iterate through the list
            list.forEachIndexed { index, color ->
                textView.append("\n${index+1}. $color")
            }
        }


        btnRetainAll.setOnClickListener {
            // Create a list with values
            val list = mutableListOf("RED","GREEN","BLACK",
                "YELLOW","WHITE","BLUE")

            // Retain only elements with name ends with 'E'
            list.retainAll{it.endsWith("E")}

            textView.text = "Retain all colors," +
                    " name ends with 'E'\n"

            // Iterate through the list
            list.forEachIndexed { index, color ->
                textView.append("\n${index+1}. $color")
            }
        }
    }
}

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/btnRemoveAll"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="removeAll"
        android:textAllCaps="false"
        app:layout_constraintBottom_toBottomOf="@+id/btnList"
        app:layout_constraintStart_toEndOf="@+id/btnList" />

    <Button
        android:id="@+id/btnRetainAll"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="retainAll"
        android:textAllCaps="false"
        app:layout_constraintBottom_toBottomOf="@+id/btnRemoveAll"
        app:layout_constraintStart_toEndOf="@+id/btnRemoveAll" />

    <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>