Dark Mode Light Mode Android Example kotlin

1/Step :  Create A New Project and Create two different theme files: one for Light Mode and another for Dark Mode.

res/values/themes.xml:

<resources>
    <style name="AppTheme" parent="Theme.Material3.Dark.NoActionBar">
        <!-- Customize your dark theme colors -->
        <item name="colorPrimary">#040E3D</item>
        <item name="colorPrimaryVariant">#B5CBDD</item>
        <item name="colorOnPrimary">#FFFFFF</item>
    </style>
</resources>

res/values-night/themes.xml:

<resources>
    <style name="AppTheme" parent="Theme.Material3.Dark.NoActionBar">
        <!-- Customize your dark theme colors -->
        <item name="colorPrimary">#BB86FC</item>
        <item name="colorPrimaryVariant">#3700B3</item>
        <item name="colorOnPrimary">#FFFFFF</item>
    </style>
</resources>

2/Step :  Add the code main_Activity.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    android:padding="16dp">

    <TextView
        android:id="@+id/themeText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Current Theme"
        android:textSize="18sp"
        android:padding="8dp" />

    <Button
        android:id="@+id/toggleButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Toggle Theme" />
</LinearLayout>

3/Step : Add the code in ManiActivity

package com.alomkaisa.myapplication

import android.content.SharedPreferences
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import androidx.activity.enableEdgeToEdge
import androidx.appcompat.app.AppCompatActivity
import androidx.appcompat.app.AppCompatDelegate
import androidx.core.view.ViewCompat
import androidx.core.view.WindowInsetsCompat

class MainActivity : AppCompatActivity() {

    private lateinit var themeText: TextView
    private lateinit var toggleButton: Button
    private lateinit var sharedPreferences: SharedPreferences

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


        themeText = findViewById(R.id.themeText)
        toggleButton = findViewById(R.id.toggleButton)


        sharedPreferences = getSharedPreferences("ThemePrefs", MODE_PRIVATE)
        val isDarkMode = sharedPreferences.getBoolean("isDarkMode", false)


        setThemeMode(isDarkMode)


        toggleButton.setOnClickListener {
            val newMode = !isDarkMode() // Toggle mode
            setThemeMode(newMode)


            with(sharedPreferences.edit()) {
                putBoolean("isDarkMode", newMode)
                apply()
            }
        }
    }

    private fun setThemeMode(isDarkMode: Boolean) {
        if (isDarkMode) {
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES)
            themeText.text = "Dark Mode"
        } else {
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO)
            themeText.text = "Light Mode"
        }
    }

    private fun isDarkMode(): Boolean {
        return sharedPreferences.getBoolean("isDarkMode", false)
    }
}