Android Kotlin: How to create and use an Enum

This code demonstrates how to create and use enums in an Android application written in Kotlin. Enums are a special kind of class that defines a set of named constants. They offer several advantages over simple string constants, including improved type safety, readability, and access to additional functionalities.

The code includes an example activity (MainActivity.kt) that showcases three different types of enums:

• A basic enum with simple constants (like Position).
• An enum with each constant holding a single additional value (like Capital).
• An enum with each constant holding multiple additional values (like Country).

The activity displays information about these enums upon clicking corresponding buttons.

Summary

By following this example, you'll gain a solid understanding of how to define and utilize enums in your Android projects. This approach enhances code maintainability, readability, and reduces the risk of errors by ensuring that only valid values can be assigned to enum variables.

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 btnBasicEnum = findViewById<Button>(R.id.btnBasicEnum)
        val btnEnumValues = findViewById<Button>(R.id.btnEnumValues)
        val btnMultiValues = findViewById<Button>(R.id.btnMultiValues)


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


        // Basic enum class
        btnBasicEnum.setOnClickListener{
            val builder = StringBuilder()
            builder.append("Basic usage of enum class")
            builder.append("\n\nPosition.Top = ${Position.Top}")
            builder.append("\nPosition.Right = ${Position.Right}")
            builder.append("\nPosition.Bottom = ${Position.Bottom}")
            builder.append("\nPosition.Left = ${Position.Left}")
            textView.text = builder.toString()
        }


        // Enum with values
        btnEnumValues.setOnClickListener{
            val builder = StringBuilder()
            builder.append("Enum with values")
            builder.append("\n\nBangladesh = ${
                Capital.Bangladesh.capital}")
            builder.append("\nIndia = ${Capital.India.capital}")
            builder.append("\nSweden = ${Capital.Sweden.capital}")
            builder.append("\nAustralia = ${
                Capital.Australia.capital}")
            builder.append("\nQatar = ${Capital.Qatar.capital}")
            textView.text = builder.toString()
        }


        // Enum with multiple values
        btnMultiValues.setOnClickListener{
            val builder = StringBuilder()
            builder.append("Enum with multiple values")
            builder.append("\n\nAustria = ${Country.Austria.capital} " +
                    ": ${Country.Austria.currency}")
            builder.append("\nChina = ${Country.China.capital} " +
                    ": ${Country.China.currency}")
            builder.append("\nEgypt = ${Country.Egypt.capital} " +
                    ": ${Country.Egypt.currency}")
            builder.append("\nFrance = ${Country.France.capital} " +
                    ": ${Country.France.currency}")
            textView.text = builder.toString()
        }
    }
}



// Basic enum class
enum class Position{
    Top, Right, Bottom, Left
}


// Enum with values
enum class Capital(val capital:String){
    Bangladesh("Dhaka"),
    India("New Delhi"),
    Sweden("Stockholm"),
    Australia("Canberra"),
    Qatar("Doha")
}


// Enum with multiple values
enum class Country(val capital:String, val currency:String){
    Austria("Vienna","Euro"),
    China("Beijing","Chinese Yuan"),
    Egypt("Cairo","Egyptian Pound"),
    France("Paris","Euro; CFP Franc")
}

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="8dp">

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

    <Button
        android:id="@+id/btnEnumValues"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="Enum Values"
        android:textAllCaps="false"
        app:layout_constraintBottom_toBottomOf="@+id/btnBasicEnum"
        app:layout_constraintStart_toEndOf="@+id/btnBasicEnum" />

    <Button
        android:id="@+id/btnMultiValues"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="Multi Values"
        android:textAllCaps="false"
        app:layout_constraintBottom_toBottomOf="@+id/btnEnumValues"
        app:layout_constraintStart_toEndOf="@+id/btnEnumValues" />

    <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/btnBasicEnum" />

</androidx.constraintlayout.widget.ConstraintLayout>