如何:实现接口事件(C# 编程指南) - C# 编程指南

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如何:实现接口事件(C# 编程指南)

发布于 2019-11-12 字数5019 浏览 974 评论 0

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。

      复制代码
    public interface IDrawingObject
    {
        event EventHandler ShapeChanged;
    }
    public class MyEventArgs : EventArgs {…}
    public class Shape : IDrawingObject
    {
        event EventHandler ShapeChanged;
        void ChangeShape()
        {
            // Do something before the event…
            OnShapeChanged(new MyEventsArgs(…));
            // or do something 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。

C#  复制代码
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.
*/

请参见

任务

如何:在派生类中引发基类事件(C# 编程指南)

概念

C# 编程指南

参考

事件(C# 编程指南)委托(C# 编程指南)显式接口实现(C# 编程指南)

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