Expressing Designs in C# - Effective C# - page 153

Handlers.Add(system, ev);
}
static public void RemoveLogger( string system,
EventHandler < LoggerEventArgs > ev)
{
// will throw exception if system
// does not contain a handler.
Handlers[system] -= ev;
}
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 messages:
l = Handlers[ "" ] as
EventHandler < LoggerEventArgs >;
if (l != null )
l( null , args);
}
}
}
The generic version trades casts and type conversions for increased code to
handle event maps. I'd prefer the generic version, but it's a close tradeoff.
Events provide a standard syntax for notifying listeners. The .NET Event
Pattern follows the event syntax to implement the Observer Pattern. Any
number of clients can attach handlers to the events and process them.
Those clients need not be known at compile time. Events don't need sub-
scribers for the system to function properly. Using events in C# decouples