以引用对象取代单例模式

    /// <summary>
    /// 封装用户输入
    /// </summary>
    public class Input
    {
        private Input() { }

        /// <summary>
        /// 用户输入实例
        /// </summary>
        private static Input _instance;

        /// <summary>
        /// 获取封装用户输入的唯一实例
        /// </summary>
        public static Input Instance
        {
            get 
            {
                if (_instance == null)
                {
                    _instance = new Input();
                }
                return _instance;
            }
        }

        /// <summary>
        /// 绑定到窗体
        /// </summary>
        /// <param name="window">相应用户输入的窗体</param>
        public void BindingToForm(Form window)
        {
            KeyBoard = new KeyBoard(window);
        }

        /// <summary>
        /// 获取或设置键盘输入状态
        /// </summary>
        public KeyBoard KeyBoard { get; private set; }

        /// <summary>
        /// 更新输入状态
        /// </summary>
        public void Update()
        {
            KeyBoard.Process();
        }
    }

    /// <summary>
    /// 封装用户输入
    /// </summary>
    public class Input
    {
        /// <summary>
        /// 绑定到窗体
        /// </summary>
        /// <param name="window">相应用户输入的窗体</param>
        public void BindingToForm(Form window)
        {
            KeyBoard = new KeyBoard(window);
        }

        /// <summary>
        /// 获取或设置键盘输入状态
        /// </summary>
        public KeyBoard KeyBoard { get; private set; }

        /// <summary>
        /// 更新输入状态
        /// </summary>
        public void Update()
        {
            KeyBoard.Process();
        }
    }

    class SpaceShip
    {
        Input _input;

        public SpaceShip(Input input)
        {
            this._input = input;
        }

        public Vector MoveDirection { get; set; }

        private Vector _posation;

        public void Move()
        {
            _posation = _posation + MoveDirection;
        }

        public void Update()
        {
            Vector amount = Vector.Zero;

            if (_input.KeyBoard.IsKeyHeld(Keys.Left))
            {
                amount.X = -1;
            }
            if (_input.KeyBoard.IsKeyHeld(Keys.Right))
            {
                amount.X = 1;
            }
            if (_input.KeyBoard.IsKeyHeld(Keys.Up))
            {
                amount.Y = -1;
            }
            if (_input.KeyBoard.IsKeyHeld(Keys.Down))
            {
                amount.Y = 1;
            }
            MoveDirection = amount;
        }
    }