# 备忘录模式

属于行为型模式。
在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态。这样以后就可以将该对象恢复到原先保存的状态。

应用场景：

缺点：消耗资源，状态数据越多，内存占用就越大。
解决方法：将数据储存到文件中（.txt、.xml、.dat 等文件），由内存占用转变为磁盘占用。

# 类图

	namespace BehavioralPatterns_MementoPattern
	{
	/// <summary>
	/// 存档
	/// </summary>
	public class Archive
	{
	private string state;
	/// <summary>
	/// 状态
	/// </summary>
	public string State { get => state; }

	public Archive(string state)
	{
	this.state = state;
	}
	}
	}

	namespace BehavioralPatterns_MementoPattern
	{
	public class ArchiveManger
	{
	private static List<Archive> Archives = new List<Archive>();

	/// <summary>
	/// 添加存档
	/// </summary>
	/// <param name="archive"></param>
	public static void AddArchive(Archive archive)
	{
	Archives.Add(archive);
	}

	/// <summary>
	/// 获取存档
	/// </summary>
	/// <param name="index"></param>
	/// <returns></returns>
	public static Archive GetArchive(int index)
	{
	return Archives[index];
	}
	}
	}

	namespace BehavioralPatterns_MementoPattern
	{
	public class Player
	{
	/// <summary>
	/// 状态
	/// </summary>
	public string State;

	public Player(string state)
	{
	State = state;
	}

	public void Show()
	{
	Console.WriteLine(State);
	}

	/// <summary>
	/// 生成存档
	/// </summary>
	/// <returns></returns>
	public Archive SaveState()
	{
	return new Archive(State);
	}

	/// <summary>
	/// 载入存档
	/// </summary>
	/// <param name="archive"></param>
	public void LoadState(Archive archive)
	{
	State = archive.State;
	}
	}
	}

	namespace BehavioralPatterns_MementoPattern
	{
	public class Program
	{
	private static void Main(string[] args)
	{
	Player player = new Player("state_0");
	player.Show();

	ArchiveManger.AddArchive(player.SaveState());

	player.State = "state_1";
	player.Show();

	player.LoadState(ArchiveManger.GetArchive(0));
	player.Show();
	}
	}
	}

运行结果：
state_0
state_1
state_0