ofb/Assets/Scripts/SceneController.cs

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

public class SceneController : MonoBehaviour
{

    // this object will always exist!
    void Awake() {
        // check to see if a state controller already exists
        if (GameObject.FindGameObjectWithTag("SceneManager") != null) {
            Destroy(this.gameObject);
        } else { // if it doesn't, then this is the only one
            this.gameObject.tag = "SceneManager";
        }
        DontDestroyOnLoad(this.gameObject);
        SceneManager.sceneLoaded += OnSceneLoaded;
    }

    void OnSceneLoaded(Scene scene, LoadSceneMode mode) {
        GameObject pauseMenu = GameObject.Find("PauseMenuCanvas");
        if (pauseMenu != null) {
            Button quitButton = GameObject.Find("QuitButton").GetComponent<Button>();
            quitButton.onClick.AddListener(BackToMainMenu);
        }
        if (scene.buildIndex == 0) { // if this is the menu
            GameObject.Find("NewGameButton").GetComponent<Button>().onClick.AddListener(NextScene);
        }
    }

    public void NextScene() {
        SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex + 1);
    }

    public void BackToMainMenu() {
        SceneManager.LoadScene(0); // main menu scene should be 0
    }

    public void LoadChosenScene(int index) {
        SceneManager.LoadScene(index);
    }

}