Decorator pattern
De Banane Atomic
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Description
- It provides a way of attaching new state and behaviour to an object dynamically.
- The object does not know it is being “decorated”.
- Decorators both inherit the original class and contain an instantiation of it.
When to use it
When you have:
- An existing component class that may be unavailable for subclassing.
You want to:
- Attach additional state or behavior to an object dynamically.
- Make changes to some objects in a class without affecting others.
- Avoid subclassing because too many classes could result.
But consider using instead:
- The Adapter pattern, which sets up an interface between different classes.
- The Composite pattern, which aggregates an object without also inheriting its interface.
- The Proxy pattern, which specifically controls access to objects.
- The Strategy pattern, which changes the original object rather than wrapping it.
Exemple
| IUser.cs |
public interface IUser
{
string Name { get; set; }
}
|
| User.cs |
public class User : IUser
{
public string Name { get; set; }
public User(string name)
{
this.Name = name;
}
}
|
| UserTitle |
public class UserTitle : IUser
{
private IUser user;
public string Name
{
get => $"{user.Name} ({Title})";
set => user.Name = value;
}
public string Title { get; set; }
public UserTitle(IUser user, string title)
{
this.user = user;
this.Title = title;
}
}
|
| UserEmail.cs |
public class UserEmail : IUser
{
private IUser user;
public string Name
{
get => $"{user.Name} - {Email}";
set => user.Name = value;
}
public string Email { get; set; }
public UserEmail(IUser user, string email)
{
this.user = user;
this.Email = email;
}
}
|
|
var user = new User("Nicolas");
Console.WriteLine(user.Name); // Nicolas
var userWithTitle = new UserTitle(user, "Big Boss");
Console.WriteLine(userWithTitle.Name); // Nicolas (Big Boss)
var userWithEmail = new UserEmail(user, "nicolas@world-company.net");
Console.WriteLine(userWithEmail.Name); // Nicolas (Big Boss) - nicolas@world-company.net
|
