.Net中的设计模式——Decorator模式

public abstract SignInDecorator:User
{
private User m_user;
public User User
{
get {return m_user;}
set {m_user = value;}
}
public override void SignIn()
{
if (m_user != null)
{
m_user.SignIn();
}
}
}

public class SecuritySignInDecorator:SignInDecorator
{
public override void SignIn()
{
if (IsValid())
{
base.SignIn();
}
else
{
throw new NotAuthorizationException();
}
}
private bool IsValid()
{
//略;
return true;
}
}
public class LoggingSignInDecorator:SignInDecorator
{
public override void SignIn()
{
base.SignIn();
Logging(); 
}
private void Logging()
{
//略;
}
}

User user = new User();
SignInDecorator securtiyDec = new SecuritySignInDecorator();
securityDec.User = user;
SignInDecorator loggingDec = new LoggingSignInDecorator();
loggingDec.User = securityDec;
loggingDec.SignIn();