这样应该看的懂吧,基本是你的思路

class Program
{
static void Main(string[] args)
{

var role = new Role() { Atk = 1000, HP = 1000 };
var weapon1 = new Weapon("刀") { };
var weapon2 = new Weapon("枪") { };
var weapon3 = new Weapon("剑") { };
role.AddWeapon(weapon1);
role.ChangeWeapon(weapon2);
role.DeleteWeapon(weapon3);
Console.ReadKey();
}
}

public class Weapon
{
public Weapon(string name)
{
this.Name = name;
}
public string Name { get; }
public int Atk { get; set; }
}

public class Role
{
private int _hp;
public int HP
{
get { return _hp; }
set
{
if (value < 0 || value > 9999) throw new Exception("设置不在范围");
_hp = value;
}
}
public int Atk { get; set; }
public string Def { get; set; }
public Weapon Weapon { get; set; }
public int GetAtk()
{
int atk = (Weapon == null) ? 0 : Weapon.Atk;
return Atk + atk;
}
public void AddWeapon(Weapon weapon) { this.Weapon = weapon; }
public void ChangeWeapon(Weapon weapon) { this.Weapon = weapon; }
public void DeleteWeapon(Weapon weapon) { this.Weapon = null; }
}