如何：实现接口事件（C# 编程指南） · MSDN C# 编程指南 & 参考手册 2015

# 如何：实现接口事件（C# 编程指南） [接口](https://msdn.microsoft.com/zh-cn/library/87d83y5b.aspx)可声明[事件](https://msdn.microsoft.com/zh-cn/library/8627sbea.aspx)。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); } } } } ``` 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. */ ``` ## 请参阅 [C# 编程指南](https://msdn.microsoft.com/zh-cn/library/67ef8sbd.aspx) [事件（C# 编程指南）](https://msdn.microsoft.com/zh-cn/library/awbftdfh.aspx) [委托（C# 编程指南）](https://msdn.microsoft.com/zh-cn/library/ms173171.aspx) [显式接口实现（C# 编程指南）](https://msdn.microsoft.com/zh-cn/library/ms173157.aspx) [如何：在派生类中引发基类事件（C# 编程指南）](https://msdn.microsoft.com/zh-cn/library/hy3sefw3.aspx)