C# 如何实现接口事件

接口可声明事件。

下面的示例演示如何在类中实现接口事件。 实现接口事件的规则与实现任何接口方法或属性的规则基本相同。

在类中实现接口事件
在类中声明事件，然后在适当的区域调用该事件。

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)
        {
            if(ShapeChanged != null)
            {
               ShapeChanged(this, e);
            }
        }
    }

}

示例
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();
        }
    }

}
/* Output:
    Sub1 receives the IDrawingObject event.
    Drawing a shape.
    Sub2 receives the IShape event.
*/

代码地址：https://download.youkuaiyun.com/download/zztoll/11014298