Model-view-controller explained
Model-view-controller (MVC) is an architectural pattern, which at the same time is also a Multitier architecture, used in software engineering. In complex computer applications that present a large amount of data to the user, a developer often wishes to separate data (model) and user interface (view) concerns, so that changes to the
user interface will not affect data handling, and that the data can be reorganized without changing the userinterface. 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.
History
The pattern was first described in 1979[1] 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: How to use Model-View-Controller.[2]
Pattern description
It is common to split an application into separate layers: presentation (UI), domain logic, 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. 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. Multiple views can exist for a single model for different purposes.
- Controller
Processes and responds to events, typically user actions, and may invoke changes on the model.
MVC is often seen in web applications, where the view is the actual HTML page, and the controller is the code that gathers dynamic data and generates the content within the HTML. 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. 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).[3]
- A view uses the model (indirectly) to generate an appropriate user interface (e.g. the 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.
- The user interface waits for further user interactions, which begins the cycle anew.
By decoupling models and views, MVC helps to reduce the complexity in architectural design, and to increase flexibility and reuse.
Selected frameworks
GUI frameworks
Java: 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 level of controls (elements of the graphical user interface). 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 (the Event dispatching thread). It catches and propagates the events to the view and model.
Web frameworks
Python: Django
The Django (web framework) web framework, among others, supports the MVC pattern, but prefers to call it *MTV*, for Model-Template-View
Combined frameworks
Java: Java Enterprise Edition (Java EE)
Unlike the other frameworks, Java EE defines a pattern for model objects.
- Model
The model is commonly represented by entity beans, although the model can be created by a servlet using a business object framework such as Spring.
- View
The view in a Java EE application may be represented by a Java Server Page, which may be currently implemented using JavaServer Faces Technology (JSF). Alternatively, 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, which may be currently implemented using JavaServer Faces (JSF).
Implementations of MVC as GUI frameworks
Smalltalk's MVC implementation inspired many other GUI frameworks, such as the following:
Visual FoxExpress is a Visual FoxPro MVC framework.
Implementations of MVC as web-based frameworks
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.
ASP
.NET
ActionScript
- ARP Usable with AIR, Flex, and Flash
- Cairngorm Usable with AIR, and Flex
- PureMVC Suitable for use with AIR, Flex, Flash, and any platform running AS3 (no non-native class dependencies)
Erlang
Java
MVC web application frameworks:
JavaScript
- CJAX A PHP-Javascript development tool for AJAX
- Archetype Javascript Framework for structuring and ease development of RIA.
- JavaScript MVC An open-source JavaScript framework for developing web applications.
- Junction A Ruby on Rails port to Javascript
Informix 4GL
Perl
- Catalyst An MVC-based avant-garde web framework.
- CGI::Application A mature, lightweight, flexible MVC framework for web application development.
- Gantry Framework A web application framework for Apache/mod_perl, CGI and Fast-CGI.
- Jifty A full-stack application framework.
- Maypole A Perl framework for MVC-oriented web applications, similar to Jakarta's Struts
- OpenInteract2 is a web application server written in Perl. It features integrated data persistence, security, user and group management, plus an easy way to create and distribute fully database-independent applications.
- PageKit A mod_perl based web application framework that uses a template system and XML.
PHP
- Joomla is MVC Framework using PHP 4.0 & 5.0
- PHP on Trax Strictly follows Ruby on Rails syntax and functionality but written in php5. Originally called PHP on Rails.
- Agavi an open-source, LGPL licensed MVC framework for creating applications written using PHP5.
- Akelos PHP Framework a Ruby on Rails port to PHP4/5.
- BareBonesMVC A one-file, no-configuration, MVC framework for PHP5.
- CakePHP webapplication framework modeled after the concepts of Ruby on Rails.
- CodeIgniter A PHP MVC framework.
- DragonPHP MVC2 Framework for PHP 5.
- Fusebox Framework for building ColdFusion and PHP web applications.
- FUSE A powerful but easy-to-use PHP 5 Framework for MVC development
- KohanaPHP A powerful, lightweight, easily extendable PHP 5 MVC Framework.
- LightVC Lightweight PHP 5 Strict MVC Framework with decoupling of Model and other non-View-Controller essentials to promote code reuse.
- MicMVC A simple framework for creating standalone MVC websites in PHP5 with RoR style models.
- Odin Assemble Small footprint PHP based MVC Framework.
- phpHtmlLib MVC based OO framework compatible with PHP4 and PHP5 licensed under GNU LGPL.
- phpXCore A MVC design pattern based PHP content management framework compatible with PHP4 and PHP5.
- PRADO A PHP 5 MVC framework.
- SilverStripe contains a fully fledged PHP 5.2 ORM/MVC Framework focused on building websites.
- Solar PHP 5 framework Solar is a PHP 5 framework for rapid application development. It is fully name-spaced and uses enterprise application design patterns, with built-in support for localization and configuration at all levels.
- OnPHP onPHP is the mature GPL'ed multi-purpose object-oriented PHP framework (plus c-module)
- Switch board with Routing PHP 5 MVC Framework with Routing.
- Jelix Framework an open source PHP 5 MVC framework designed for highly performance.
- Symfony Framework PHP 5 MVC Framework.
- TinyMVC Framework Simple and lightweight PHP5 MVC (Model-View-Controller) framework.
- TYPO3 extension library lib/div PHP 4/5 MVC framework for TYPO3 extension development
- Qcodo is an open-source PHP 5 web application framework
- Zend Framework A PHP 5-based MVC framework.
- ZNF PHP5 MVC framework for enterprise web applications
- Zoop Framework A Mature PHP 4/5 MVC framework.
- Lion Framework An open-source PHP 5 framework with a push & pull MVC implementation
Python
Ruby
See also
References
- http://heim.ifi.uio.no/~trygver/themes/mvc/mvc-index.html
- http://st-www.cs.uiuc.edu/users/smarch/st-docs/mvc.html
- Complex controllers are often structured using the command pattern to encapsulate actions and simplify extension.
External links
General information regarding MVC
