Which are C# native built-in design patterns?

Question

Which design patterns are build-in supported by C# regardless framework version? I'm thinking of patterns such as Observer pattern that can be found in interface IObservable. ObservableCollection, INotifyPropertyChanged etc.

Please provide with the namespace of the pattern in your answers!

For quite a long time I was thinking that extension methods implement the decorator pattern, but they don't: Decorator overrides and extends existing methods transparently whilst extension methods add new methods to an existing class. Still I'd be interested in whether there is a design pattern for that! — chiccodoro, Oct 28 '10 at 08:56

jgauffin · Accepted Answer · 2021-08-27T07:54:09.867

27

Action<T> (normally used as visitor pattern)

Discover the Design Patterns You're Already Using in the .NET Framework (MSDN Magazine)

Example

public class Root
{
    //Private and not exposed in a IList property = Encapsulation
    private List<Node> _nodes = new List<Node>(); 

    public void Accept(Action<Node> visitor)
    {
        // Controlled enumeration, can for instance handle exceptions in here.
        foreach (var item in _nodes)
        {
            visitor(node);
        }
    }
}

// usage
root.Accept(node => Console.WriteLine(node));

edited Aug 27 '21 at 07:54

answered Oct 28 '10 at 08:31

jgauffin

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The link is now broken, but it's in the Wayback Machine: https://web.archive.org/web/20120814171359/http://msdn.microsoft.com/en-us/magazine/cc188707.aspx - OP, could you please update the post? – jmdon Jul 25 '18 at 14:56
@jmdon: Done. thanks. Added a small example as a bonus. – jgauffin Jul 26 '18 at 07:16
Shouldn't the method be called `Accept()` as is tradition? – Dmitri Nesteruk Aug 27 '21 at 07:16

score 11 · Answer 2 · answered Mar 05 '15 at 02:26

Creational Patterns

Abstract Factory

System.Data.Common.DbProviderFactory

Builder

System.Text.StringBuilder
System.Data.Common.DbConnectionStringBuilder

Factory Method

System.Activator
System.Net.WebRequest

Prototype

System.ICloneable

Singleton

System.StringComparer.InvariantCulture
System.StringComparer.InvariantCultureIgnoreCase

Structural Patterns

Adapter

System.IO.StreamReader

Bridge

System.Globalization.CultureInfo

Composite

System.ComponentModel.IComponent

Decorator

System.IO.Stream

Facade

System.Environment
System.String

Flyweight

System.StringComparer

Proxy

System.Net.WebClient
System.Runtime.Remoting.Proxies.RealProxy
System.ServiceModel.ICommunicationObject

Behavioral Patterns

Chain Of Responsibility

Microsoft.Practices.EnterpriseLibrary.Logging.Logger

Command

System.Windows.RoutedEventArgs

Interpreter

System.IFormatProvider
System.Text.RegularExpressions.Regex

Iterator

System.Collections.IEnumerable
System.Data.IDataReader

Mediator

System.Threading.Timer

Memento

System.Runtime.Serialization.ISerializable

Observer

System.EventHandler
System.IObservable

State

??

Strategy

System.Collections.Generic.IComparer

Template Method

System.Web.UI.Page

Visitor

System.Linq.Expressions.ExpressionVisitor

The inclusion of `ICloneable` above is incorrect. A prototype is expected to provide a deep, not shallow, copy of an object. — Dmitri Nesteruk, Oct 08 '19 at 06:14

score 6 · Answer 3 · answered Oct 28 '10 at 08:29

6

Iterator is one (all collection classes and arrays can use the foreach statement for iteration).

Another is the observer pattern - pretty much this is what events are. In 4.0 the IObservable and ObservableCollection were added.

answered Oct 28 '10 at 08:29

Oded

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Oren A · Answer 4 · 2010-10-28T08:48:30.153

4

StringBuilder uses the builder design pattern..
And there is the DbDataAdapter class (adapter pattern).
The Null Object pattern is broadly used as well.

edited Oct 28 '10 at 08:48

answered Oct 28 '10 at 08:41

Oren A

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score 4 · Answer 5 · answered Oct 28 '10 at 14:37

Observer pattern. All our events and delegates are raised through the observer pattern.

Factory pattern. Connection strings and db providers from factory.

Iterator Pattern: Ienumerable, Ienumerators in our foreach statements

Adapter: COM communication. Runtime Callable Wrappers(RCW)

Template: Used in several places esp in ASP.NET classes where you can override to provide new implementation

Proxy: For all our webservice calls. in c# 3.0 we got proxy collections as well.

There could be many more. But these are the ones that came to my mind

score 3 · Answer 6 · edited Jun 20 '20 at 09:12

3

Abstract Factory: System.Data.Common.DbProviderFactory

edited Jun 20 '20 at 09:12

Community

1
1

answered Oct 28 '10 at 08:35

Ruben

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score 0 · Answer 7 · answered Oct 28 '10 at 08:33

0

The delegation pattern (that's what the delegates and expresssions are for)

answered Oct 28 '10 at 08:33

Adrian Grigore

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score 0 · Answer 8 · answered Oct 28 '10 at 08:38

0

The proxy pattern is used often.

answered Oct 28 '10 at 08:38

Which are C# native built-in design patterns?

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