Model-view-controller

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A simple diagram depicting the relationship between the Model, View, and Controller. Note: the solid lines indicate a direct association, and the dashed line indicate an indirect association (e.g., observer pattern).

Model-view-controller (MVC) is an architectural pattern used in software engineering. In complex computer applications that present lots of data to the user, one often wishes to separate data (model) and user interface (view) concerns, so that changes to the user interface do not impact the data handling, and that the data can be reorganized without changing the user interface. The model-view-controller solves this problem by decoupling data access and business logic from data presentation and user interaction, by introducing an intermediate component: the controller.

[edit] Pattern description

It is common to split an application into separate layers: presentation (UI), domain, and data access. In MVC the presentation layer is further separated into view and controller. MVC encompasses more of the architecture of an application than is typical for a design pattern.

Model: The domain-specific representation of the information on which the application operates. It is a common misconception that the model is another name for the domain layer. Domain logic adds meaning to raw data (e.g., calculating if today is the user's birthday, or the totals, taxes and shipping charges for shopping cart items).; Many applications use a persistent storage mechanism (such as a database) to store data. MVC does not specifically mention the data access layer because it is understood to be underneath or encapsulated by the Model.
View: Renders the model into a form suitable for interaction, typically a user interface element.
Controller: Processes and responds to events, typically user actions, may invoke changes on the model.

MVC is often seen in web applications, where the view is the actual HTML page and the code which gathers dynamic data and generates the content within the HTML is the controller. Finally the model is represented by the actual content, usually stored in a database or XML-files.

Though MVC comes in different flavors, control flow generally works as follows:

The user interacts with the user interface in some way (e.g., user presses a button)
A controller handles the input event from the user interface, often via a registered handler or callback.
The controller accesses the model, possibly updating it in a way appropriate to the user's action (e.g., controller updates user's shopping cart).^[1]
A view uses the model to generate an appropriate user interface (e.g., view produces a screen listing the shopping cart contents). The view gets its own data from the model. The model has no direct knowledge of the view. (However, the observer pattern can be used to allow the model to indirectly notify interested parties – potentially including views – of a change.)
The user interface waits for further user interactions, which begins the cycle anew.

[edit] Implementations

The pattern was first described in 1979 by Trygve Reenskaug, then working on Smalltalk at Xerox research labs. The original implementation is described in depth in the influential paper Applications Programming in Smalltalk-80(TM):How to use Model-View-Controller.

Smalltalk's MVC implementation inspired many other GUI frameworks such as:

Adobe AS2/3.
The NeXTSTEP and OPENSTEP development environments encourage the use of MVC. Cocoa and GNUstep, based on these technologies, also use MVC.
The Core Data framework is the most powerful MVC implementation for the Apple Macintosh to date. It is a modern addition to Cocoa frameworks and is fully supported by the latest Xcode IDE.
Microsoft Foundation Classes (MFC) (called Document/View architecture here)
Java Swing
JFace
The Qt Toolkit since Qt4 Release.
XForms has a clear separation of model (stored inside the HTML head section) from the presentation (stored in the HTML body section). XForms uses simple bind commands to link the presentation to the model.
Web template systems (see list of implementation on article) are widely used on web and other contexts. It is a kind of "view subsystem" in a MVC
Business Server Pages (BSP) in SAP
Joomla 1.5 (CMS) http://www.joomla.org

[edit] MVC in various languages

[edit] .NET

[edit] ASP.NET

In ASP.NET, the patterns for the view and controller are not well defined. The model is left to the developer to design, views and controls can be created in a variety of ways.

Model: ASP.NET does not strictly require a model. The developer has the option to create a model class, but may choose to forget it and have the event handlers in the controller perform any calculations and data persistence. That said, using a model to encapsulate business rules and database access is both possible and preferable.

View: The ASPX and ASCX files generally handle the responsibilities of the view, although it can also come from compiled server controls. With this pattern, the view object actually inherits from the controller object. This is different from the Smalltalk implementation, in which separate classes have pointers to one another.

Controllers: The duties of the controller are split between two places. The generation and passing of events is part of the framework and more specifically the Page and Control classes. The handling of events is usually done in the code-behind class. However, moving code specific to the transition between views in a separate Controller is a good practice. In turn, it becomes possible to centralize the registration of Observers in the isolated Controller.

[edit] Windows Forms

In WinForms, a .NET framework, the patterns for the view and controller are well defined. The model is left to the developer to design.

Model: Just like ASP.Net, WinForms does not strictly require a model. The developer has the option to create a model class, but may choose to forget it and have the event handlers in the controller perform any calculations and data persistence. Again, using a model to encapsulate business rules and database access is both possible and preferable. It is left to developers to design the Model

View: A class inheriting from either Form or Control handles the responsibilities of the view. In the case of WinForms, the View and Controller are compiled into the same class. This differs from ASP.Net, which uses inheritance, and Smalltalk, which have separate classes with pointers to one another.

Controller: The duties of the controller are split between three places. The generation and passing of events starts at the OS level. Inside the .Net framework, the Form and Control classes route the event to the proper event handler. The handling of events is usually done in the code-behind class how it can be changed.

[edit] .NET MVC Frameworks

MonoRail is a MVC Web Framework inspired by Action Pack from Ruby on Rails.
The Spring.NET is an application framework focused on helping build enterprise .NET applications.
Maverick.NET is a .NET port of Maverick, a Model-View-Controller (aka "Model 2") framework for web publishing.

[edit] Java

[edit] Java Platform, Enterprise Edition (Java EE)

Unlike the other frameworks, Java EE defines a pattern for model objects.

Model: The model is represented by entity beans.

View: The view in a Java EE application may be represented by a Java Server Page. Alternately, the code to generate the view may be part of a servlet.

Controller: The controller in a Java EE application may be represented by a servlet.

[edit] Java MVC Frameworks

Struts is one of the original web-application frameworks which makes extensive use of MVC logic.
WebWork is a MVC Java web-application development framework. It is built specifically with developer productivity and code simplicity in mind, providing robust support for building reusable UI templates, such as form controls, UI themes, internationalization, dynamic form parameter mapping to JavaBeans, robust client and server side validation, and much more.
The Spring Framework is a newer J2EE application framework for both native Java applications as well as Java-served web-applications. Spring utilizes a multi-tier approach to java applications. One of the layers enables struts-like MVC implementations.
Java Server Faces (JSF) framework is one of the most advanced, Java standardized web-application frameworks.
Swing (see below)
JFace, a MVC framework built on the Eclipse project's SWT set of operating-system-native controls

[edit] Java Swing

Java Swing is different from the other frameworks, in that it supports two MVC patterns.

Model (Frame level): Like the other frameworks, the design of the real model is usually left to the developer.

Model (Control level): Swing also supports models on the control level. Unlike other frameworks, Swing exposes the internal storage of each control as a model.

View: The view is represented by a class that inherits from Component.

Controller: Java Swing doesn't necessarily use a single controller. Because its event model is based on interfaces, it is common to create an anonymous action class for each event. In fact, the real controller is in a separate thread. It catches and propagates the events to the view and model.

[edit] Ruby

The Nitro and Ruby on Rails web frameworks are popular Model-view-controller architectures for Ruby.

[edit] Python

Python has many MVC frameworks. The two most popular frameworks are Django and TurboGears.

[edit] Perl

The most popular MVC for Perl is Catalyst. Catalyst borrows from other frameworks such as Ruby on Rails and Apache Struts. It makes extensive use of the CPAN archive to provide the various components as follows.

Model

Catalyst is very flexible on the Model, examples being DBIx::Class, Class::DBI, Class::DBI::SQLite

View

CPAN modules such as Template Toolkit, Mason, HTML::Template, XSLT and Petal can all be used as the View.

Controller

Catalyst uses advanced URL to action dispatching to map the URL to the correct controller.

[edit] PHP

There are many different MVC frameworks for PHP, some of which seek to imitate framework features from Java, .NET, and elsewhere. PHP Frameworks like CakePHP, Symphony, PHPOnTrax implement the MVC pattern. Often the Smarty template language is used to separate presentation from program logic. Zend, the primary company behind the development of PHP, recently began developing an MVC framework for PHP. Symfony is a newer rapid/development MVC framework that mimics some of the best features on Rails and Django. Joomla version 1.5 uses an MVC model throughout its web-application framework.

[edit] ColdFusion

ColdFusion also does not have a built in MVC structure, but has many third-party frameworks such as Model-Glue, Fusebox and Mach-II which stress the MVC ideal

[edit] Architectures for Web-based Interfaces

In the design of web applications, MVC is implemented by web template systems as "View for web" component.

MVC is also known as a "Model 2" architecture in Sun parlance. Complex web applications continue to be more difficult to design than traditional applications, and MVC is being pushed as a potential solution to these difficulties.

The external links in this article may require cleanup to comply with Wikipedia's content policies.
Please improve this article by removing excessive or inappropriate external links. Please remove this tag when this is done. (talk)

AJILE - A JavaScript module that supports MVC via the separation of HTML and JavaScript.
Akelos Framework - A PHP version of Ruby on Rails MVC Framework.
Apache Cocoon - use the pyramid of contracts concept, to the separation of content, style, logic and management functions.
ASWing An opensource actionscript2 (Flash) implementation of the Java Swing library.
Blokz A PHP + PostgreSQL MVC Framework.
CakePHP A MVC and Active Records design pattern based PHP framework
Camping is a Microframework
Catalyst
Code Igniter A PHP MVC framework
Copix - PHP Framework
Django
DragonPHP
Ingenious MVC .Net MVC
Fusebox
JavaServer Faces, Apache Struts and Webwork2 are currently the most popular web oriented MVC implementations.
Igloo (Experimental) MVC Framework for .Net 2.0
Joomla! v 1.5 A PHP MVC application framework
Mach-II
Maverick for .Net
Maypole
Microsoft UIP
Model-Glue for ColdFusion Link
MonoRail An ActionPack inspired MVC framework from the Castle Project
Nitro
OpenXava Business component oriented as alternative to classical MVC frameworks
Orbeon
MVC frameworks written in PHP (Wiki)
Phrame
PHP on Trax
phpXCore A MVC design pattern based PHP content management framework
PRADO - PRADO is a component-based and event-driven framework
Radicore For either PHP 4 or 5
Ruby on Rails
Sanders - MVC framework based on Mojavi 3
Smart3
Solarphp - PHP framework under development
Solstice - An MVC-based Perl web application framework.
Spring Framework
Stripes
Struts
Switch board - PHP 5 MVC Framework with Routing
Symfony
Tapestry
TurboGears for python, with AJAX
The WebObjects development/deployment environment is strongly based on MVC.
Wicket
Witango rapid application development tool based on XML and a C++ server engine. Easily ports code to Java.
XForms is an approach on building web based applications based on MVC, under development by W3C
Zend Framework A light-weight framework for PHP.
ZNF
Zoop Framework A Mature PHP 4/5 MVC Framework

[edit] See also

Trygve Reenskaug
Architectural patterns
Model 1
Three-tier (computing)
Model-View-Presenter (MVP) design pattern
The Observer design pattern
The Template Method design pattern
The Presentation-abstraction-control (PAC) pattern (a strict version of the Hierarchical-Model-View-Controller (HMVC))

[edit] External links

General information regarding MVC

Specific aspects of MVC or alternatives to MVC

Core J2EE Patterns - Front Controller
Holub, Allen. "Building user interfaces for object-oriented systems", Java World, 1999.
Gresh, John E.. "The Collection Switch Design Pattern", Rensselaer Computer Science Seminar, 2004, 2004.
MVC versus "Event Driven" Discussion
What's a Controller Anyway
GUI Architectures article by Martin Fowler.

MVC frameworks in PHP

Zend Framework A PHP 5 based MVC framework. Zend Framework
Zoop Framework A Mature PHP 4/5 MVC framework. Zoop Framework
Symfony Framework PHP 5 MVC Framework. Symfony Framework
Switch Board with Routing PHP 5 MVC Framework with Routing. Switch board.
CakePHP, webapplication framework modeled after the concepts of Ruby on Rails. CakePHP.
PHP on Trax (PDF), a presentation by John Peterson, creator of Trax
MVC Frameworks for PHP (PDF), a presentation on general MVC principles, especially as applied to PHP
The Model-View-Controller Design Pattern for PHP an implementation which utilises reusable XSL stylesheets for the View.
Odin Assemble Small footprint PHP based MVC Framework
phpXCore MVC Framework for PHP. Compatible with PHP4 and PHP5. phpXCore Framework

[edit] References

^ Complex controllers are often structured using the command pattern to encapsulate actions and simplify extension.

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