Proxy in VB.NET

Provide a surrogate or placeholder for another object to control access to it. Proxy pattern provides a representative object (proxy) that controls access to another similar object.

Please download project with this source code from https://github.com/ViacheslavUKR/StandardDisignOopPattern

   1:      ' Proxy Design Pattern.

   2:      ' See description in //www.vb-net.com/ProgramTheory/Proxy.htm

   3:      Class MainApp

   4:          ' Entry point into console application.

   5:          Public Shared Sub Main()

   6:              ' Create proxy and request a service

   7:              Dim proxy As New Proxy()

   8:              proxy.Request()

   9:              ' Wait for user

  10:              Console.ReadKey()

  11:          End Sub

  12:      End Class

  13:      ' The 'Subject' abstract class

  14:      MustInherit Class Subject

  15:          Public MustOverride Sub Request()

  16:      End Class

  17:   

  18:      ' The 'RealSubject' class

  19:      Class RealSubject

  20:          Inherits Subject

  21:          Public Overrides Sub Request()

  22:              Console.WriteLine("Called RealSubject.Request()")

  23:          End Sub

  24:      End Class

  25:   

  26:      ' The 'Proxy' class

  27:      Class Proxy

  28:          Inherits Subject

  29:          Private _realSubject As RealSubject

  30:          Public Overrides Sub Request()

  31:              ' Use 'lazy initialization'

  32:              If _realSubject Is Nothing Then

  33:                  _realSubject = New RealSubject()

  34:              End If

  35:              _realSubject.Request()

  36:          End Sub

  37:      End Class

• Abstract Factory in VB.NET - Creates an instance of several families of classes.
• Builder in VB.NET - Separates object construction from its representation.
• Factory Method in VB.NET - Creates an instance of several derived classes.
• Prototype in VB.NET - A fully initialized instance to be copied or cloned.
• Singleton in VB.NET - A class of which only a single instance can exist.

• Adapter in VB.NET - Match interfaces of different classes
• Bridge in VB.NET - Separates an object’s interface from its implementation
• Composite in VB.NET - A tree structure of simple and composite objects
• Decorator in VB.NET - Add responsibilities to objects dynamically
• Facade in VB.NET - A single class that represents an entire subsystem
• Flyweight in VB.NET - A fine-grained instance used for efficient sharing
• Proxy in VB.NET - An object representing another object

• Chain of Resp. in VB.NET - A way of passing a request between a chain of objects
• Command in VB.NET - Encapsulate a command request as an object
• Interpreter in VB.NET - A way to include language elements in a program
• Iterator in VB.NET - Sequentially access the elements of a collection
• Mediator in VB.NET - Defines simplified communication between classes
• Memento in VB.NET - Capture and restore an object's internal state
• Observer in VB.NET - A way of notifying change to a number of classes
• State in VB.NET - Alter an object's behavior when its state changes
• Strategy in VB.NET - Encapsulates an algorithm inside a class
• Template Method in VB.NET - Defer the exact steps of an algorithm to a subclass
• Visitor in VB.NET - Defines a new operation to a class without change

Theory context:

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