C# 标准事件流实例代码

服装价格变动，触发淘宝发布活动和消费者购买衣服事件流

public class EventStandard
  {
    public class Clothes {

      /// <summary>
      /// 服装编码
      /// </summary>
      public string Id { get; set; }

      /// <summary>
      /// 服装名称
      /// </summary>
      public string Name { get; set; }

      /// <summary>
      /// 服装价格
      /// </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>
      /// 服装价格变动事件
      /// </summary>
      public event EventHandler PriceRiseHandler;

    }

    /// <summary>
    /// 衣服价格事件参数 一般会为特定的事件去封装个参数类型
    /// </summary>
    public class PriceEventArgs : EventArgs
    {
      public double OldPrice { get; set; }
      public double NewPrice { get; set; }
    }

    public class TaoBao {
      /// <summary>
      /// 淘宝订户
      /// </summary>
      public void PublishPriceInfo(object sender, EventArgs e) {
        Clothes clothes = (Clothes)sender;
        PriceEventArgs args = (PriceEventArgs)e;
        if (args.NewPrice < args.OldPrice)
          Console.WriteLine($"淘宝：发布衣服价格下降的公告，{clothes.Name}服装直降{args.OldPrice - args.NewPrice}元，限时抢购！");
        else
          Console.WriteLine("淘宝：价格悄悄上涨或价格未变化，啥也不做");
      }

    }

    public class Consumer
    {
      /// <summary>
      /// 消费者订户
      /// </summary>
      public void Buy(object sender, EventArgs e)
      {
        Clothes clothes = (Clothes)sender;
        PriceEventArgs args = (PriceEventArgs)e;
        if (args.NewPrice < args.OldPrice)
          Console.WriteLine($"消费者：之前价格{args.OldPrice}，现在价格{args.NewPrice},果断买了！");
        else
          Console.WriteLine($"消费者：等等看，降价了再说");
      }
    }

    public static void Show()
    {
      Clothes clothes = new Clothes()
      {
        Id = "12111-XK",
        Name = "优衣库",
        Price = 128
      };
      //订阅：把订户和发布者的事件关联起来
      clothes.PriceRiseHandler += new TaoBao().PublishPriceInfo;
      clothes.PriceRiseHandler += new Consumer().Buy;
      //价格变化，自动触发订户订阅的事件
      clothes.Price = 300;
    }

  }

调用：

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

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

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