如何：實現介面事件（C# 編程指南）

 

C# 編程指南

如何：實現介面事件（C# 編程指南）

 介面可聲明事件。下面的樣本示範如何在類中實現介面事件。介面事件的實現規則與任何介面方法或屬性的實現規則基本相同。在類中實現介面事件在類中聲明事件，然後在適當的位置調用該事件。 複製代碼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);        }    }}樣本下面的樣本示範如何處理以下的不常見情況：您的類是從兩個以上的介面繼承的，每個介面都含有同名事件）。在這種情況下，您至少要為其中一個事件提供明確介面實作。為事件編寫明確介面實作時，必須編寫 add 和 remove 事件訪問器。這兩個事件訪問器通常由編譯器提供，但在這種情況下編譯器不能提供。您可以提供自己的訪問器，以便指定這兩個事件是由您的類中的同一事件表示，還是由不同事件表示。例如，根據介面規範，如果事件應在不同時間引發，則可以將每個事件與類中的一個單獨實現關聯。在下面的樣本中，訂戶將形狀引用強制轉換為 IShape 或 IDrawingObject，從而確定自己將會接收哪個 OnDraw 事件。 C#複製代碼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    publicclass Shape : IDrawingObject, IShape    {        // Create an event for each interface event        event EventHandler PreDrawEvent;        event EventHandler PostDrawEvent;         // Explicit interface implementation required.        // Associate IDrawingObject's event with        // PreDrawEvent        event EventHandler IDrawingObject.OnDraw        {            add { PreDrawEvent += value; }            remove { PreDrawEvent -= value; }        }        // Explicit interface implementation required.        // Associate IShape's event with        // PostDrawEvent        event EventHandler IShape.OnDraw        {            add { PostDrawEvent += value; }            remove { PostDrawEvent -= value; }        }         // For the sake of simplicity this one method        // implements both interfaces.         publicvoid 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());            }        }    }    publicclass 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    publicclass 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.");        }    }      publicclass Program    {        staticvoid Main(string[] args)        {            Shape shape = new Shape();            Subscriber1 sub = new Subscriber1(shape);            Subscriber2 sub2 = new Subscriber2(shape);            shape.Draw();             Console.WriteLine("Press Enter to close this window.");            Console.ReadLine();        }    } }輸出Sub1 receives the IDrawingObject event.Drawing a shape.Sub2 receives the IShape event.  (來源：msdn )