UISettings.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Audio;
using UnityEngine.UI;

public class UISettings : MonoBehaviour {

    public AudioMixer audioMixer;

    public Dropdown resolutionsDropdown;
    public Toggle fullScreenToggle;

    Vector2Int[] resolutions;

    void Start() {
        resolutions = new Vector2Int[3];
        resolutions[0] = new Vector2Int(800, 600);
        resolutions[1] = new Vector2Int(1024, 768);
        resolutions[2] = new Vector2Int(1366, 768);
    }

    public void SetResolution(int resolutionIndex) {
        Vector2Int resolution = resolutions[resolutionIndex];
        Screen.SetResolution(resolution.x, resolution.y, Screen.fullScreen);
    }

    public void SetVolume(float volume) {
        audioMixer.SetFloat("volume", volume);
    }

    public void SetQuality(int qualityIndex) {
        QualitySettings.SetQualityLevel(qualityIndex);
    }

    public void SetFullscreen(bool isFullscreen) {
        Screen.fullScreen = isFullscreen;
    }

    public void OnExit() {
        #if UNITY_EDITOR
        UnityEditor.EditorApplication.isPlaying = false;
        #else
        Application.Quit();
        #endif
    }
}