dark mode kotlin

MainActivity.kt

 package com.example.constrainttutorial

import android.content.SharedPreferences
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import androidx.appcompat.app.AppCompatDelegate

 class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        /**
         * save the settings of the dark mode by using shared preferences
         */
        val appSettingsPref: SharedPreferences = getSharedPreferences("appSettings", 0)
        val isNightMode: Boolean = appSettingsPref.getBoolean("NightMode", false)
        val sharedPrefEdit: SharedPreferences.Editor = appSettingsPref.edit()


        /**
         * check whether isNightMode is true. if it is enable dark mode else disable it
         */
        if (isNightMode){
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES)
        } else{
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
        }
        var buttonMode = findViewById<Button>(R.id.mode_button)
        
        /**
         * When the button is clicked if night mode is true disable it and put the value in our shared preferences
         */
        buttonMode.setOnClickListener {
            if (isNightMode){
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
                sharedPrefEdit.putBoolean("NightMode", false).apply()
            } else{
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES)
                sharedPrefEdit.putBoolean("NightMode", true).apply()
            }

        }
    }
}