Create Buttons.cs

using System;
using System.Collections.Generic;
using UniRx;
using UnityEngine;

namespace BirdStrike.Vista.UI.TitleScene.Model
{
    public class MainMenuManager : MonoBehaviour
    {
        private Subject<ActionCommand[]> _commandSubject = new Subject<ActionCommand[]>();

        public IObservable<ActionCommand[]> CommandSubject => _commandSubject;

        private readonly Stack<ActionCommand[]> _commandStack = new Stack<ActionCommand[]>();

        void Start()
        {
            RegisterCommand(_ => new[]
            {
                new ActionCommand("設定", () => Debug.Log("A")),
                new ActionCommand("設定2", () =>
                {
                    RegisterCommand(prev => new[]
                    {
                        new ActionCommand("もどる", () => RegisterCommand(__ => prev)),
                    });
                }),
            });
        }


        private void RegisterCommand(Func<ActionCommand[], ActionCommand[]> commands)
        {
            var p = _commandStack.Count > 0 ? _commandStack.Pop() : new ActionCommand[0];
            var c = commands(p);
            _commandStack.Push(c);
            _commandSubject.OnNext(c);
        }
    }

    public struct ActionCommand
    {
        public ActionCommand(string name, Action command)
        {
            Name = name;
            Command = command;
        }

        public string Name { get; }
        public Action Command { get; }
    }
}