CLR Via CSharp读书笔记（11）：事件

事件实现简洁版：

public event EventHandler<MailEventArgs> NewMail;

protected virtual void OnNewMail(MailEventArgs e) {
    EventHandler<MailEventArgs> temp = Interlocked.CompareExchange(ref NewMail, null, null);
    if (temp != null)
    {
        temp(this, e);
    }
}

public void SimulateNewMail(String from, String to, String subject)
{
    MailEventArgs e = new MailEventArgs(from, to, subject);
    OnNewMail(e);
}

事件注册：

多个事件实现：

public sealed class EventSet {
   // The private dictionary used to maintain EventKey -> Delegate mappings
   private readonly Dictionary<EventKey, Delegate> m_events =
       new Dictionary<EventKey, Delegate>();

   // Adds an EventKey -> Delegate mapping if it doesn't exist or 
   // combines a delegate to an existing EventKey
   public void Add(EventKey eventKey, Delegate handler) {
      Monitor.Enter(m_events);
      Delegate d;
      m_events.TryGetValue(eventKey, out d);
      m_events[eventKey] = Delegate.Combine(d, handler);
      Monitor.Exit(m_events);
   }

   // Removes a delegate from an EventKey (if it exists) and 
   // removes the EventKey -> Delegate mapping the last delegate is removed
   public void Remove(EventKey eventKey, Delegate handler) {
      Monitor.Enter(m_events);
      // Call TryGetValue to ensure that an exception is not thrown if
      // attempting to remove a delegate from an EventKey not in the set
      Delegate d;
      if (m_events.TryGetValue(eventKey, out d)) {
         d = Delegate.Remove(d, handler);

         // If a delegate remains, set the new head else remove the EventKey
         if (d != null) m_events[eventKey] = d;
         else m_events.Remove(eventKey);
      }
      Monitor.Exit(m_events);
   }

   // Raises the event for the indicated EventKey
   public void Raise(EventKey eventKey, Object sender, EventArgs e) {
      Delegate d;
      Monitor.Enter(m_events);
      m_events.TryGetValue(eventKey, out d);
      Monitor.Exit(m_events);

      if (d != null) {
         d.DynamicInvoke(new Object[] { sender, e });
      }
   }
}