Are there any design patterns used in the .NET Framework?

Question

I would like to know: are any GoF design patterns are used in the .NET Framework?

BOUNTY:

I have seen the MSDN link below in an answer. Are there any post/video or can you can list patterns and most importantly WHERE it is used?

Answer 1

The .NET framework uses many of the Gang of Four patterns. Here are just a few examples:

Creational patterns

• Abstract Factory: System.Data.Common.DbProviderFactory. Every member function of this class is a factory method.
• Builder: The WCF channel construction infrastructure.
• Factory Method:
  • System.Data.IDbConnection.BeginTransaction(). The type of transaction created depends on the underlying IDbConnection implementation.
  • WebRequest.Create() returns a concrete type that depends on the URL scheme.
• Prototype - used in framework for cloning and serialization
• Singleton - used as an activation method in WCF, i.e. a web service may be treated as a singleton by the WCF infrastructure. Ditto for .NET Remoting.

Structural patterns

• Adapter: The ADO.NET providers, eg System.Data.SqlClient.SqlConnection, System.Data.OleDb.OleDbConnection etc. Each provider is an adapter for its specific database.
• Composite: many examples
  • System.Windows.Forms.Control and its derived classes.
  • System.Web.UI.Control and its derived classes.
  • System.Xml.XmlNode and its derived classes.
• Decorator:
  • System.Windows.Controls.Decorator (in WPF).
  • Some implementations of Stream are decorators around an inner stream (e.g. GZipStream, CryptoStream).
• Facade: System.Xml.Serialization.XmlSerializer. XmlSerializer hides a complex task (that includes generating assemblies on the fly!) behind a very easy-to-use class.
• Proxy: The web service proxies generated by svcutil.exe and deriving from System.ServiceModel.ClientBase<TChannel>

Behavioral Patterns

• Chain of responsibility: System.Web.UI.Control.OnBubbleEvent() and System.Web.UI.Control.RaiseBubbleEvent().
• Command:System.Windows.Input.ICommand (in WPF).
• Interpreter: System.Linq.Expressions.Expression and related classes.
• Iterator: many examples
  • System.Collections.IEnumerable.
  • System.Collections.Generic.IEnumerable<T>.
  • System.Data.IDataReader.
• Memento: The .NET Serializable pattern is a variation on the Memento pattern.
• Observer - The .NET event mechanism.
• Strategy - Sort method in ArrayList
• Template Method - Render method for custom controls
• Visitor : System.Linq.Expressions.ExpressionVisitor (used internally by [LINQ])