理解：1.确保只有一个实例 2.提供一个全局访问点，大白话就是：不能在其他类new 出来；

代码：

using System;

namespace SingletonDemo
{
//角色类，单例模式
class Player{
//字段
public string name;
public int hp;
public int Mhp;
public int level;

//共有属性
//共有方法
public void BeAttack(){
hp -= 10;
if(hp<=0){
Console.WriteLine ("die");
}
}

public void GetExp(){
level++;
if (level >= 2) {
hp++;
Console.WriteLine ("life add one");
}
}
//3.提供实例的接口（可以是属性，或方法）
public static Player GetInstance(){
if(null==_instance){
_instance = new Player ();
}
return _instance;
}
//1.私有化构造方法
private Player(){

}
//2.类的内部提供一个静态实例
private static Player _instance;

}
//背包类
class Bag{
public void GetLife(){

Player p = Player.GetInstance ();
p.hp += 10;
p.hp = p.hp > p.Mhp ? p.Mhp : p.hp;

}
}
class MainClass
{

public static void Main (string[] args)
{

Player p = Player.GetInstance ();
p.name="jack";
p.hp = 50;
p.Mhp = 100;
p.level = 1;
Bag bag = new Bag ();
bag.GetLife ();
Console.WriteLine ("Player Name:"+p.name+" Player HP:"+p.hp+" Level:"+p.level);
p.BeAttack ();
p.GetExp ();
Console.WriteLine ("Player Name:"+p.name+" Player HP:"+p.hp+" Level:"+p.level);
Console.ReadKey ();

}
}
}

C# 单例模式