Expressing Designs in C# - Effective C# - page 147

are built on delegates to provide type-safe function signatures for event
handlers. Add to this the fact that most examples that use delegates are
events, and developers start thinking that events and delegates are the same
things. In Item 24, I showed you examples of when you can use delegates
without defining events. You should raise events when your type must
communicate with multiple clients to inform them of actions in the sys-
tem. Events are how objects notify observers.
Consider a simple example. You're building a log class that acts as a dis-
patcher of all messages in an application. It will accept all messages from
sources in your application and will dispatch those messages to any inter-
ested listeners. These listeners might be attached to the console, a data-
base, the system log, or some other mechanism. You define the class as
follows, to raise one event whenever a message arrives:
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
{