Menu Manager - yaSingleton Example - Unity 2018 Tutorial

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using yaSingleton;

[CreateAssetMenu(fileName="MenuManager", menuName="Systems/MenuManager")]
public class MenuManager : Singleton<MenuManager> {

    // public GameObject pauseMenuPrefab;
    public GameObject pauseMenuPrefab;
    public GameObject saveMenuPrefab;
    public GameObject canvasPrefab;
    private Canvas _canvas;
    private List<GameMenu> activeMenus;

    protected override void Initialize() {
        base.Initialize();
        activeMenus = new List<GameMenu>();
    }

    public Canvas SceneCanvas {
        get {
            // Check if canvas variable is set
            if(_canvas == null) {
                // If not set, look in scene for canvas
                _canvas = FindObjectOfType<Canvas>();

                if(_canvas == null) {
                    // If no canvas in scene, create one
                    _canvas = Instantiate(canvasPrefab).GetComponent<Canvas>();
                }
            }

            // Return canvas
            return _canvas;
        }
    }

    public void CreateMenu(GameMenu menu) {
        // Creates a new game menu
        GameObject newMenu = Instantiate(menu.gameObject, SceneCanvas.transform);
        GameMenu menuComponent = newMenu.GetComponent<GameMenu>();
        System.Type type = menuComponent.GetType();

        if(type == typeof(PauseMenu)) {
            AddPauseMenuFunctionality((PauseMenu) menuComponent);
        } else if(type == typeof(SaveMenu)) {
            AddSaveMenuFunctionality((SaveMenu) menuComponent);
        }

        // Assign functionality to the buttons
        menuComponent.destroyMenuButton.onClick.AddListener(
            delegate { DestroyMenu(menuComponent); }
        );

        activeMenus.Add(menu);
    }

    public void AddPauseMenuFunctionality(PauseMenu pauseMenu) {
        pauseMenu.openSaveMenuButton.onClick.AddListener(
                delegate { ValidateAndCreateMenuPrefab(saveMenuPrefab); }
            );
        pauseMenu.openSaveMenuButton.onClick.AddListener(
            delegate { DestroyMenu(pauseMenu); }
        );
    }

    public void AddSaveMenuFunctionality(SaveMenu saveMenu) {

    }

    public void DestroyMenu(GameMenu menu) {
        if(menu != null) {
            activeMenus.Remove(menu);
            Destroy(menu.gameObject);
        }
    }

    /// <summary>
    /// Checking if the prefab has a GameMenu script.
    /// If so, then instantiate the prefab.
    /// </summary>
    /// <param name="prefab"></param>
    private void ValidateAndCreateMenuPrefab(GameObject prefab) {
        // Escape is down
        GameMenu menu = prefab.GetComponent<GameMenu>();

        if(menu != null) {
            CreateMenu(menu);
        } else {
            Debug.LogError("Pause Menu Prefab has no GameMenu script attached to it.");
        }
    }

    public override void OnUpdate() {
        if(Input.GetKeyDown(KeyCode.Escape)) {
            bool exists = false;

            // Checking to see if one exists
            foreach(GameMenu menu in activeMenus) {
                if(menu.GetType() == typeof(PauseMenu)) {
                    exists = true;
                    break;
                }
            }

            if(!exists) {
                // Escape is down
                ValidateAndCreateMenuPrefab(pauseMenuPrefab);
            }
        }
    }


}