如何實作介面事件 (C# 程式設計指南)

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介面可以宣告事件。 下列範例示範如何在類別中實作介面事件。 基本上，規則與您在實作任何介面方法或屬性時相同。

在類別中實作介面事件

在類別中宣告事件，然後在適當的區域中加以叫用。

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);  
        }  
    }  

}

範例

下列範例示範如何處理以下較不常見的狀況：您的類別繼承自兩個或多個介面，且每個介面具有相同名稱的事件。 在此情況下，您必須針對其中至少一個事件提供明確介面實作。 當您針對事件撰寫明確介面實作時，也必須撰寫 add 和 remove 事件存取子。 這些通常是由編譯器所提供的，但在此案例中，編譯器無法提供它們。

您可以提供自己的存取子，來指定是否要透過類別中的相同事件或透過不同的事件來表示這兩個事件。 例如，如果根據介面規格應該在不同時間引發事件，則可以將每個事件與類別中的個別實作產生關聯。 在下列範例中，訂閱者會藉由將圖形參考轉換為 IShape 或 IDrawingObject，來判斷他們將接收哪些 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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