实现接口事件

在类中实现接口事件

可以在接口中声明事件，然后在类中实现该事件的引用。在为方法订阅事件时，可以订阅接口声明的事件，也可以订阅类中的事件。

class InterfaceEvent
{

static void Main(string[] args)
{
Shape s = new Shape();
IDrawingObject ido = s;
//为HandlerShapeChanged方法订阅接口中声明的事件
ido.ShapeChanged += HandlerShapeChanged;

//为HandlerShapeChanged方法订阅实现接口的事件
s.ShapeChanged += HandlerShapeChanged;
s.ChangeShape();

Console.Read();
}

static void HandlerShapeChanged(object sender, CustomEventArgs e)
{
Console.WriteLine("Received event.Shape area is now {0}", e.Area);
}
}
public class CustomEventArgs : EventArgs
{
private double area;
public double Area
{
get { return area; }
set { area = value; }
}
public CustomEventArgs(double a)
{
area = a;
}
}
public interface IDrawingObject
{
event EventHandler<CustomEventArgs> ShapeChanged;
}
public class Shape : IDrawingObject
{
public event EventHandler<CustomEventArgs> ShapeChanged;
public void ChangeShape()
{
OnShapeChanged(new CustomEventArgs(10));
}
protected virtual void OnShapeChanged(CustomEventArgs e)
{
EventHandler<CustomEventArgs> hander = ShapeChanged;
if (hander != null)
{
hander(this, e);
}
}
}

输出如下：



事件访问器

事件访问器类似属性访问器，事件访问器被命名为add和remove，一般情况下不需提供自定义事件访问器，因为在编译时会自动添加事件访问器。

add事件访问器：当客户端订阅该事件，调用该访问器。

remove事件访问器：当客户端取消订阅事件，调用该访问器。

class Events : IDrawingObject
{
event EventHandler PreDrawEvent;

event EventHandler IDrawingObject.OnDraw
{
add
{
lock (PreDrawEvent)
{
PreDrawEvent += value;
}
}
remove
{
lock (PreDrawEvent)
{
PreDrawEvent -= value;
}
}
}

}

类继承同名事件声明的多个接口

当类继承多个接口，接口中有同名事件声明，则需要借助add和remove事件访问器显示接口实现。

class TwoInterfaceEvent
{
static void Main(string[] args)
{
Shape shape = new Shape();
Subscriber1 sub1 = new Subscriber1(shape);
Subscriber2 sub2 = new Subscriber2(shape);
shape.Draw();

Console.Read();
}
}

public interface IDrawingObject
{
event EventHandler OnDraw;
}

public interface IShape
{
event EventHandler OnDraw;
}

public class Shape : IDrawingObject, IShape
{
event EventHandler PreDrawEvent;
event EventHandler PostDrawEvent;

object objectLock = new object();

/// <summary>
/// 明确接口实现
/// PreDrawEvent与IDrawingObject.OnDraw关联
/// </summary>
event EventHandler IDrawingObject.OnDraw
{
add
{
lock (objectLock)
{
PreDrawEvent += value;
}
}
remove
{
lock (objectLock)
{
PreDrawEvent -= value;
}
}
}

/// <summary>
/// 明确接口实现
/// PostDrawEvent与IShape.OnDraw关联
/// </summary>
event EventHandler IShape.OnDraw
{
add
{
lock (objectLock)
{
PostDrawEvent += value;
}
}
remove
{
lock (objectLock)
{
PostDrawEvent -= value;
}
}
}

/// <summary>
/// 同时引用两个接口事件
/// </summary>
public void Draw()
{
//引用事件PreDrawEvent
EventHandler handler = PreDrawEvent;
if (handler != null)
{
handler(this, new EventArgs());
}
Console.WriteLine("Raised IDrawingObject's event.");

//引用事件PostDrawEvent
handler = PostDrawEvent;
if (handler != null)
{
handler(this, new EventArgs());
}
Console.WriteLine("Raised IShape's event.");
}

}

public class Subscriber1
{
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.");
}
}
public class Subscriber2
{
public Subscriber2(Shape shape)
{
IShape s = (IShape)shape;
s.OnDraw+=new EventHandler(s_OnDraw);
}
void s_OnDraw(object sender, EventArgs e)
{
Console.WriteLine("Sub2 receives the IShape event.");
}
}

输出如下：