DaveAndAl.net Do Application Design Patterns Make Sense in ASP.NET? Alex Homer You may like to write these down now

DaveAndAl.net Agenda What are Design Patterns? Basic Design Patterns for ASP.NET Basic Pattern Support within ASP.NET Controller Patterns for ASP.NET Advanced Patterns for ASP.NET Conclusion and Summary

DaveAndAl.net Design Patterns are Scary...!

DaveAndAl.net You Use Patterns Every Day... try { something } catch (SqlException qx) { handle SQL error } catch (SecurityException sx) { handle security violation } catch (Exception ex) { handle all other exceptions } finally { clean up resources } Using xr As XmlReader = XmlReader.Create("file.xml")... read some XML... End Using Structured Exception Handling Factory Lifetime

DaveAndAl.net What are Design Patterns? Informal Design Patterns Code constructs, best practice, well- structured, common sense, the accepted approach, evolved over time Formal Design Patterns Documented as "Context", "Problem", "Solution", and a UML diagram Have specific aims Solve specific issues

DaveAndAl.net Why Do We Need Design Patterns? Engineering disciplines require patterns Structural Engineering Electronic Engineering... even Social Engineering! Creating software is also Engineering Structural design and architecture Componentization and interconnections User interface design and implementation Deployment, testing, and management

DaveAndAl.net Formal Design Patterns "Fundamental to any science or engineering discipline is a common vocabulary for expressing its concepts, and a language for relating them together." "... a body of literature to help software developers resolve recurring problems encountered throughout all of software development." "... a shared language for communicating insight and experience about these problems and their solutions." from

DaveAndAl.net The Gang of Four (GOF) Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides "Design Patterns: Elements of Reusable Object-Oriented Software" (1995) The Hillside Group

DaveAndAl.net Microsoft.NET Design Patterns "Enterprise Solution Patterns Using Microsoft.NET" From the patterns and practices (p&p) Group Printed book (ISBN: ) PDF Download 1C38E-ABFC-484F-A076-CF99B

DaveAndAl.net.NET Design Pattern Frameworks "data & object factory" Design Pattern Framework Ingenious MVC for.NET 2.0 Web and WinForms Microsoft "patterns & practices" Group CAB and ObjectBuilder Enterprise Library Software Factories (Smart Client, Mobile, Web Service)

DaveAndAl.net Pattern Types and Families These are just a few of the common ones... PatternShare.org lists more than 250 !

DaveAndAl.net Common Patterns in ASP.NET Model-View-Controller (MVC) Model-View-Presenter (MVP) Use Case Controller Command Publish-Subscribe / Observer Plug-in / Module / Intercepting Filter Service Agent / Proxy / Broker Provider / Adapter Factory / Builder / Injection Singleton Repository Presentation Logic Host or Behavioral Creational Structural Persistence

DaveAndAl.net Agenda What are Design Patterns? Basic Design Patterns for ASP.NET Basic Pattern Support within ASP.NET Controller Patterns for ASP.NET Advanced Patterns for ASP.NET Conclusion and Summary

DaveAndAl.net MVC & MVP Presentation Patterns Both improve reusability of business logic MVC has dependency between model and view MVP improves testability but adds complexity

DaveAndAl.net Provider / Adapter Patterns Used by ASP.NET itself, and other frameworks such as Enterprise Library Allows behavioral changes without prior knowledge of requirements

DaveAndAl.net Service Agent / Proxy / Broker Removes dependencies between client and service through intermediate brokers Range of different implementations, with or without service agent logic component

DaveAndAl.net Repository Persistence Pattern Virtualizes storage of an entity in a persistent medium, such as a database or as XML Hides storage implementation from the application code

DaveAndAl.net Singleton Creation Pattern Provides for creation of a class for which only a single instance can exist Useful for exposing read-only data Useful for exposing static methods that do not rely on instance data Include private default constructor to prevent client instantiation Provide a static GetInstance method that returns the current instance

DaveAndAl.net Agenda What are Design Patterns? Basic Design Patterns for ASP.NET Basic Pattern Support within ASP.NET Controller Patterns for ASP.NET Advanced Patterns for ASP.NET Conclusion and Summary

DaveAndAl.net Pattern Support within ASP.NET

DaveAndAl.net Pattern Support within ASP.NET

DaveAndAl.net Pattern Support within ASP.NET

DaveAndAl.net Pattern Support within ASP.NET

DaveAndAl.net Pattern Support within ASP.NET

DaveAndAl.net How To... MVP: use ASP.NET code-behind model or extend code file with custom classes Provider: use built-in providers or create custom providers from a base class or interface Repository: typed DataSet, third-party tools (such as CodeSmith), or custom code Adapter: use built-in (such as CSS control adapters) or create custom adapters Service Agent and Proxy: Web References in Visual Studio, maybe wrap in custom class

DaveAndAl.net Basic Patterns in ASP.NET Example

DaveAndAl.net Agenda What are Design Patterns? Basic Design Patterns for ASP.NET Basic Pattern Support within ASP.NET Controller Patterns for ASP.NET Advanced Patterns for ASP.NET Conclusion and Summary

DaveAndAl.net Use Case Controller Coordinates and sequences interaction between the system and the users to carry out a process

DaveAndAl.net Page Controller & Front Controller Select content to display in a page using different partial views, or... Select which page (view) to display

DaveAndAl.net Plug-in/Module/Intercepting Filter Allows the features or behavior of an application to change when it loads separate components that implement extra functionality Plug-ins and Modules may be custom assemblies (modules), or general-purpose software components such as ActiveX controls or Java applets Intercepting Filters reside in an application pipeline, such as the ASP.NET HTTP pipeline Commonly, the components extend the features of the host application

DaveAndAl.net Implementation in ASP.NET HTTP Module performs redirection at front Page Controller selects view elements

DaveAndAl.net How To... Use Case: custom branching code in presenter class - case statements using Server.Transfer, or displaying partial Views as User Controls Page Controller: custom base class for Page that handles Init or Load event to perform common tasks then calls a method in the actual page to create page-specific content Front Controller: an HTTP Module that adds a custom handler to a pipeline event that performs the appropriate Server.Transfer

DaveAndAl.net Page & Front Controller Example

DaveAndAl.net Agenda What are Design Patterns? Basic Design Patterns for ASP.NET Basic Pattern Support within ASP.NET Controller Patterns for ASP.NET Advanced Patterns for ASP.NET Conclusion and Summary

DaveAndAl.net Factory / Builder / Injection Separates the construction of a complex object from its representation Allows use of the same construction process to create different representations In the Factory pattern, the subclasses of the object generator determine the object type In the Builder and Injection patterns, the client passes instructions or hints to the object generator to specify the required object type.

DaveAndAl.net Command Design Pattern Separates command invoker and receiver

DaveAndAl.net Observer and Publish/Subscribe Separates creator and receiver(s) of events

DaveAndAl.net Command-Observer Implementation Client creates and subscribes objects

DaveAndAl.net Command-Observer Implementation Introduces a dependency between Observer and Subject, but removes the requirement for events

DaveAndAl.net Command-Observer Example

DaveAndAl.net Observer and Publish/Subscribe Separates creator and receiver(s) of events

DaveAndAl.net Publish-Subscribe Example

DaveAndAl.net Conclusions - 1 MVP and the various Controller patterns are useful, but firing update events from Model usually is not. Page Controller and Front Controller allow for custom use case behavior by showing different views or activating different presenters. Front Controller can make use of the Intercepting Filter pattern. Repository is useful for virtualization of source data. Singleton is useful for reducing the need for multiple instances. Service Agent and Proxy are ideal for interacting with remote services.

DaveAndAl.net Conclusions - 2 Provider is useful for accessing various types of data sources. Adapter is useful for extending ASP.NET controls. Factory, Builder, Injection, Observer, and Command are probably less useful, more complex, and can be difficult to implement. Event-driven patterns like Publish-Subscribe are generally useful only if all subscribers are instantiated within the page lifetime. The composite Command-Observer event-free approach is useful for removing dependencies between classes.

DaveAndAl.net References Information about Design Patterns: us/dnpag/html/intpatt.asp Contact: Slides & code: Article: