c#怎样实现接口事件

时间:2020-10-13 olprod 人气:0

接口可以声明事件。下面的示例演示如何在类中实现接口事件。这些规则基本上都与实现任何接口方法或属性时的相同。

在类中实现接口事件

在类中声明事件，然后在相应区域中调用它。

namespace ImplementInterfaceEvents 
{ 
  public interface IDrawingObject 
  { 
    event EventHandler ShapeChanged; 
  } 
  public class MyEventArgs : EventArgs
  { 
    // class members 
  } 
  public class Shape : IDrawingObject 
  { 
    public event EventHandler ShapeChanged; 
    void ChangeShape() 
    { 
      // Do something here before the event… 

      OnShapeChanged(new MyEventArgs(/*arguments*/)); 

      // or do something here after the event.
    } 
    protected virtual void OnShapeChanged(MyEventArgs e) 
    { 
      ShapeChanged?.Invoke(this, e); 
    } 
  } 

}

示例

下面的示例演示如何处理不太常见的情况：类继承自两个或多个接口，且每个接口都具有相同名称的事件。在这种情况下，你必须为至少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，还必须编写 add 和 remove 事件访问器。通常这些访问器由编译器提供，但在这种情况下编译器不提供它们。

通过提供自己的访问器，可以指定两个事件是由类中的同一个事件表示，还是由不同事件表示。例如，如果根据接口规范应在不同时间引发事件，可以在类中将每个事件与单独实现关联。在下面的示例中，订阅服务器确定它们通过将形状引用转换为 IShape 或 IDrawingObject 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
    #region IDrawingObjectOnDraw
    event EventHandler IDrawingObject.OnDraw
    {
      add
      {
        lock (objectLock)
        {
          PreDrawEvent += value;
        }
      }
      remove
      {
        lock (objectLock)
        {
          PreDrawEvent -= value;
        }
      }
    }
    #endregion
    // 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.
      PreDrawEvent?.Invoke(this, EventArgs.Empty);

      Console.WriteLine("Drawing a shape.");

      // Raise IShape's event after the object is drawn.
      PostDrawEvent?.Invoke(this, EventArgs.Empty);
    }
  }
  public class Subscriber1
  {
    // References the shape object as an IDrawingObject
    public Subscriber1(Shape shape)
    {
      IDrawingObject d = (IDrawingObject)shape;
      d.OnDraw += 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 += 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();
    }
  }
}
/* Output:
  Sub1 receives the IDrawingObject event.
  Drawing a shape.
  Sub2 receives the IShape event.
*/

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