事件是用来通知观察者来进行相应的操作，其经常被用来在事件的发送者和接受者间进行解耦，事件的机制也是用观察者模式来实现的。下面是一组事件参数（LoggerEventArgs）和定义事件属性类(Logger类中定义了Log事件)的代码：
public class LoggerEventArgs : EventArgs
{
public string Message { get; private set; }
public int Priority { get; private set; }
public LoggerEventArgs(int p, string m)
{
Priority = p;
Message = m;
}
}
public class Logger
{
static Logger()
{
theOnly = new Logger();
}
private Logger()
{
}
private static Logger theOnly = null;
public static Logger Singleton
{
get { return theOnly; }
}
// Define the event:
public event EventHandler<LoggerEventArgs> Log;
/* 上面事件的定义其实可以解析为下面的代码
private EventHandler<LoggerEventArgs> log;
public event EventHandler<LoggerEventArgs> Log
{
add { log = log + value; }
remove { log = log - value; }
}
*/
// add a message, and log it.
public void AddMsg(int priority, string msg)
{
// 这里构建了一个临时变量来缓存事件的引用，没有直接引用Log事件引用，这样在多线程调用中就不会出现在调用前，Log事件被其他线程去除的冲突问题
EventHandler<LoggerEventArgs> l = Log;
if (l != null)
l(this, new LoggerEventArgs(priority, msg));
}
}
自定义一个多系统事件统一处理类
public class Logger
{
//利用Dictionary<string,T>范型集合来构建键值对形式（系统名称,事件委托声明）的事件集合,这里的T是EventHandler<LoggerEventArgs>的事件类型
private static Dictionary<string, EventHandler<LoggerEventArgs>> Handlers =
new Dictionary<string, EventHandler<LoggerEventArgs>>();
/// <summary>
/// 添加日志事件
/// </summary>
/// <param name="system">系统名称</param>
/// <param name="ev">事件声明</param>
static public void AddLogger(string system, EventHandler<LoggerEventArgs> ev)
{
if (Handlers.ContainsKey(system))
Handlers[system] += ev;
else
Handlers.Add(system, ev);
}
/// <summary>
/// 移除日志事件
/// </summary>
/// <param name="system">系统名称</param>
/// <param name="ev">事件声明</param>
static public void RemoveLogger(string system,EventHandler<LoggerEventArgs> ev)
{
// will throw exception if system
// does not contain a handler.
Handlers[system] -= ev;
}
/// <summary>
/// 添加日志信息
/// </summary>
/// <param name="system">系统名称</param>
/// <param name="priority">优先级</param>
/// <param name="msg">消息名称</param>
static public void AddMsg(string system,int priority, string msg)
{
if (string.IsNullOrEmpty(system))
{
EventHandler<LoggerEventArgs> l = null;
Handlers.TryGetValue(system, out l);
LoggerEventArgs args = new LoggerEventArgs(priority, msg);
if (l != null)
l(null, args);
// The empty string means receive all message
l = Handlers[""] as EventHandler<LoggerEventArgs>;
if (l != null)
l(null, args);
}
}
}