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

Model-view-controller (MVC) is an architectural pattern used in software engineering. Successful use of the pattern isolates business logic from user interface considerations, resulting in an application where it is easier to modify either the visual appearance of the application or the underlying business rules without affecting the other. In MVC, the Model represents the information (the data) of the application and the business rules used to manipulate the data, the View corresponds to elements of the user interface such as text, checkbox items, and so forth, and the Controller manages details involving the communication to the model of user actions such as keystrokes and mouse movements.

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[edit] History

The pattern was first described in 1979[1] by Trygve Reenskaug, then working on Smalltalk at Xerox PARC. The original implementation is described in depth in the influential paper Applications Programming in Smalltalk-80: How to use Model-View-Controller.[2]

After that numerous derivatives of the MVC pattern appeared. Probably one of the most known of them is the Model View Presenter pattern, which appeared in the early 90s and was designed to be an evolution of mvc(model view controller) However Model-View-Controller still remains very popular and widely used.

[edit] 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 in XML nodes, and the business rules that transform that content based on user actions.

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

  1. The user interacts with the user interface in some way (e.g. presses a button).
  2. A controller handles the input event from the user interface, often via a registered handler or callback.
  3. The controller notifies the model of the user action, possibly resulting in a change in the model's state. (e.g. controller updates user's Shopping cart).[3]
  4. 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.
  5. 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.

[edit] Selected frameworks

[edit] GUI frameworks

[edit] Java: Java Swing

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

Model

Frame level model-- Like other frameworks, the design of the real model is usually left to the developer.
Control level model-- 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.

[edit] Combined frameworks

[edit] 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).

[edit] 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.

[edit] 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 typically implemented as a "Model 2" architecture in Sun parlance. Model2 focuses on efficiently handling and dispatching full page form posts and reconstructing the full page via a front controller. Complex web applications continue to be more difficult to design than traditional applications because of this "full page" effect. More recently AJAX driven frameworks that focus on firing focused UI events at specific UI Components on the page are emerging. This is causing MVC to be revisited for web application development using traditional desktop programming techniques.

[edit] .NET

[edit] ActionScript

[edit] ASP

[edit] ColdFusion

[edit] Erlang

[edit] Java

MVC web application frameworks:

[edit] JavaScript

  • CJAX Rajesh ascript 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.
  • JamalA Javascript framework built on top of jQuery.
  • DojoMVCA Dojo based MVC framework that integrates Dojo and jQuery.

[edit] Informix 4GL

[edit] Object-Pascal

  • Powtils Ongoing development on a new MVC library for web programming with Object-Pascal (FreePascal, Delphi etc).

[edit] 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.

[edit] PHP

  • Agavi an open-source, LGPL licensed MVC framework for creating applications written using PHP5.
  • AGLite Framework Simple, easy and flexible framework for PHP.
  • 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.
  • Drupal Community plumbing: open source modular framework and content management system.
  • FLOW3 A PHP5 / PHP6 based enterprise application framework, with MVC, Dependency Injection, Aspect-Oriented Programming and more.
  • FUSE A powerful but easy-to-use PHP 5 Framework for MVC development
  • Fusebox Framework for building ColdFusion and PHP web applications.
  • Jelix Framework an open source PHP 5 MVC framework designed for highly performance.
  • KohanaPHP A powerful, lightweight, easily extendable PHP 5 MVC Framework.
  • Kumbia Framework Simple, easy and flexible framework for PHP.
  • LightVC Lightweight PHP 5 Strict MVC Framework with decoupling of Model and other non-View-Controller essentials to promote code reuse.
  • Lion Framework An open-source PHP 5 framework with a push & pull MVC implementation
  • MicMVC A simple framework for creating standalone MVC websites in PHP5 with RoR style models.
  • Odin Assemble Small footprint PHP based MVC Framework.
  • OnPHP onPHP is the mature GPL'ed multi-purpose object-oriented PHP framework (plus c-module)
  • PHP on Trax Strictly follows Ruby on Rails syntax and functionality but written in php5. Originally called PHP on Rails.
  • 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.
  • PureMVC Framework for PHP
  • Qcodo is an open-source PHP 5 web application 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.
  • Switch board with Routing PHP 5 MVC Framework with Routing.
  • 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
  • XPT Framework A PHP 5 MVC 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.
  • Zym Framework A Zend Framework extension

[edit] Python

[edit] Ruby

[edit] See also

[edit] References

  1. ^ http://heim.ifi.uio.no/~trygver/themes/mvc/mvc-index.html
  2. ^ How to use Model-View-Controller (MVC)
  3. ^ Complex controllers are often structured using the command pattern to encapsulate actions and simplify extension.

[edit] External links

General information regarding MVC