public class EventStandard
  {
    public class Clothes {

      /// <summary>
      /// 服裝編碼
      /// </summary>
      public string Id { get; set; }

      /// <summary>
      /// 服裝名稱
      /// </summary>
      public string Name { get; set; }

      /// <summary>
      /// 服裝價格
      /// </summary>
      private double _price;

      public double Price {
        get { return this._price; }
        set {
            PriceRiseHandler?.Invoke(this, new PriceEventArgs()
            {
              OldPrice = this._price,
              NewPrice = value
            });
          this._price = value;
        }
      }

      /// <summary>
      /// 服裝價格變動事件
      /// </summary>
      public event EventHandler PriceRiseHandler;

    }

    /// <summary>
    /// 衣服價格事件參數(shù) 一般會為特定的事件去封裝個參數(shù)類型
    /// </summary>
    public class PriceEventArgs : EventArgs
    {
      public double OldPrice { get; set; }
      public double NewPrice { get; set; }
    }

    public class TaoBao {
      /// <summary>
      /// 淘寶訂戶
      /// </summary>
      public void PublishPriceInfo(object sender, EventArgs e) {
        Clothes clothes = (Clothes)sender;
        PriceEventArgs args = (PriceEventArgs)e;
        if (args.NewPrice < args.OldPrice)
          Console.WriteLine($"淘寶：發(fā)布衣服價格下降的公告，{clothes.Name}服裝直降{args.OldPrice - args.NewPrice}元，限時搶購！");
        else
          Console.WriteLine("淘寶：價格悄悄上漲或價格未變化，啥也不做");
      }

    }

    public class Consumer
    {
      /// <summary>
      /// 消費者訂戶
      /// </summary>
      public void Buy(object sender, EventArgs e)
      {
        Clothes clothes = (Clothes)sender;
        PriceEventArgs args = (PriceEventArgs)e;
        if (args.NewPrice < args.OldPrice)
          Console.WriteLine($"消費者：之前價格{args.OldPrice}，現(xiàn)在價格{args.NewPrice},果斷買了！");
        else
          Console.WriteLine($"消費者：等等看，降價了再說");
      }
    }

    public static void Show()
    {
      Clothes clothes = new Clothes()
      {
        Id = "12111-XK",
        Name = "優(yōu)衣庫",
        Price = 128
      };
      //訂閱：把訂戶和發(fā)布者的事件關聯(lián)起來
      clothes.PriceRiseHandler += new TaoBao().PublishPriceInfo;
      clothes.PriceRiseHandler += new Consumer().Buy;
      //價格變化，自動觸發(fā)訂戶訂閱的事件
      clothes.Price = 300;
    }

  }

clothes.Price = 300; 
EventStandard.Show();

clothes.Price = 98; 
EventStandard.Show();