结合.net框架在C#派生类中触发基类事件及实现接口事件

下面的示例演示如何处理以下的不常见情况：您的类是从两个以上的接口继承的，每个接口都含有同名事件）。在这种情况下，您至少要为其中一个事件提供显式接口实现。为事件编写显式接口实现时，必须编写 add 和 remove 事件访问器。这两个事件访问器通常由编译器提供，但在这种情况下编译器不能提供。
您可以提供自己的访问器，以便指定这两个事件是由您的类中的同一事件表示，还是由不同事件表示。例如，根据接口规范，如果事件应在不同时间引发，则可以将每个事件与类中的一个单独实现关联。在下面的示例中，订户将形状引用强制转换为 IShape 或 IDrawingObject，从而确定自己将会接收哪个 OnDraw 事件。

namespace WrapTwoInterfaceEvents
{
  using System;

  public interface IDrawingObject
  {
    // Raise this event before drawing
    // the object.
    event EventHandler OnDraw;
  }
  public interface IShape
  {
    // Raise this event after drawing
    // the shape.
    event EventHandler OnDraw;
  }


  // Base class event publisher inherits two
  // interfaces, each with an OnDraw event
  public class Shape : IDrawingObject, IShape
  {
    // Create an event for each interface event
    event EventHandler PreDrawEvent;
    event EventHandler PostDrawEvent;

    object objectLock = new Object();

    // Explicit interface implementation required.
    // Associate IDrawingObject's event with
    // PreDrawEvent
    event EventHandler IDrawingObject.OnDraw
    {
      add
      {
        lock (objectLock)
        {
          PreDrawEvent += value;
        }
      }
      remove
      {
        lock (objectLock)
        {
          PreDrawEvent -= value;
        }
      }
    }
    // Explicit interface implementation required.
    // Associate IShape's event with
    // PostDrawEvent
    event EventHandler IShape.OnDraw
    {
      add
      {
        lock (objectLock)
        {
          PostDrawEvent += value;
        }
      }
      remove
      {
        lock (objectLock)
        {
          PostDrawEvent -= value;
        }
      }


    }

    // For the sake of simplicity this one method
    // implements both interfaces. 
    public void Draw()
    {
      // Raise IDrawingObject's event before the object is drawn.
      EventHandler handler = PreDrawEvent;
      if (handler != null)
      {
        handler(this, new EventArgs());
      }
      Console.WriteLine("Drawing a shape.");

      // RaiseIShape's event after the object is drawn.
      handler = PostDrawEvent;
      if (handler != null)
      {
        handler(this, new EventArgs());
      }
    }
  }
  public class Subscriber1
  {
    // References the shape object as an IDrawingObject
    public Subscriber1(Shape shape)
    {
      IDrawingObject d = (IDrawingObject)shape;
      d.OnDraw += new EventHandler(d_OnDraw);
    }

    void d_OnDraw(object sender, EventArgs e)
    {
      Console.WriteLine("Sub1 receives the IDrawingObject event.");
    }
  }
  // References the shape object as an IShape
  public class Subscriber2
  {
    public Subscriber2(Shape shape)
    {
      IShape d = (IShape)shape;
      d.OnDraw += new EventHandler(d_OnDraw);
    }

    void d_OnDraw(object sender, EventArgs e)
    {
      Console.WriteLine("Sub2 receives the IShape event.");
    }
  }


  public class Program
  {
    static void Main(string[] args)
    {
      Shape shape = new Shape();
      Subscriber1 sub = new Subscriber1(shape);
      Subscriber2 sub2 = new Subscriber2(shape);
      shape.Draw();

      // Keep the console window open in debug mode.
      System.Console.WriteLine("Press any key to exit.");
      System.Console.ReadKey();
    }
  }

}

								 
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