如何：实现接口事件（C# 编程指南）
更新：2007 年 11 月
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。
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。
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.
*/