如何：實現接口事件（C# 編程指南） · MSDN C# 編程指南 & 參考手冊 2015

# 如何：實現接口事件（C# 編程指南） [接口](https://msdn.microsoft.com/zh-cn/library/87d83y5b.aspx)可聲明[事件](https://msdn.microsoft.com/zh-cn/library/8627sbea.aspx)。下面的示例演示如何在類中實現接口事件。實現接口事件的規則與實現任何接口方法或屬性的規則基本相同。 ## 在類中實現接口事件 * 在類中聲明事件，然后在適當的區域調用該事件。 ``` 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); } } } } ``` 下面的示例演示如何處理以下的不常見情況：您的類是從兩個以上的接口繼承的，每個接口都含有同名事件）。在這種情況下，您至少要為其中一個事件提供顯式接口實現。為事件編寫顯式接口實現時，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，根據接口規范，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。在下面的示例中，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。 ``` 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. */ ``` ## 請參閱 [C# 編程指南](https://msdn.microsoft.com/zh-cn/library/67ef8sbd.aspx) [事件（C# 編程指南）](https://msdn.microsoft.com/zh-cn/library/awbftdfh.aspx) [委托（C# 編程指南）](https://msdn.microsoft.com/zh-cn/library/ms173171.aspx) [顯式接口實現（C# 編程指南）](https://msdn.microsoft.com/zh-cn/library/ms173157.aspx) [如何：在派生類中引發基類事件（C# 編程指南）](https://msdn.microsoft.com/zh-cn/library/hy3sefw3.aspx)