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.

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. However Model-View-Controller still remains very widely used.

Pattern description

Model-view-controller is both an architectural pattern and a design pattern, depending on where it is used.

As an architectural pattern

It is common to split an application into separate layers that run on different computers: presentation (UI), domain logic, and data access. In MVC the presentation layer is further separated into view and controller.

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.

Some implementations such as the w3c XForms also use the concept of a dependency graph to automate the updating of views when data in the model changes.

By decoupling models and views, MVC helps to reduce the complexity in architectural design, and to increase flexibility and reuse.

As a design pattern

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 whether 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.

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 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.

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).

XForms

Model

XForms stores the Model as XML in the browser.

View

The Views are XForms controls for screen elements and can be placed directly in a web page.

The model and views are bound together using reference or binding statements. These binding statements are used by the XForms dependancy graph to ensure that the correct views are updated when data in the model changes.

Controller

All mouse events are processed by XForms controls and XML events are dispatched.

Implementations of MVC as GUI frameworks

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

• Core Data framework in Mac OS X, a modern addition to Cocoa.
• GNUstep, based on these technologies, also use MVC.
• GTK+
• JFace
• MFC (called Document/View architecture here)
• Nextstep development environments encourage the use of MVC. Cocoa
• OpenStep development environments encourage the use of MVC. Cocoa
• Qt since Qt4 Release.
• Java Swing
• Adobe Flex
• Wavemaker open source, browser-based development tool based on MVC
• WPF uses a similar Model-view-viewmodel pattern.
• 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 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.

.NET

• ASP.NET MVC Framework
• Maverick.NET
• Monorail An ActionPack inspired MVC framework from the Castle Project

ColdFusion

• Mach-II A framework that focuses on trying to ease software development and maintenance
• Model-Glue Through a simple implementation of Implicit Invocation and Model-View-Controller, they allow applications to be well organized without sacrificing flexibility.
• FuseBox Fusebox does not force the Model-View-Controller (MVC) pattern or Object-Oriented Programming (OOP) on the developer. However, either or both of these development approaches can be used with Fusebox.

Java

MVC web application frameworks:

• Aranea
• Cocoon
• Grails
• Google Web Toolkit
• Oracle Application Framework
• Spring MVC Framework
• Struts
• Stripes
• Tapestry
• WebObjects
• WebWork
• Wicket
• JSF

JavaScript

MVC web application frameworks:

• SproutCore
• Wavemaker WYSIWYG development platform for Ajax web applications^[4]
• DojoMVC JavaScript MVC based upon Dojo core. Includes jQuery integration.

ABAP Objects

• BSP
• Web Dynpro ABAP

Informix 4GL

• Informix 4GL MVC models to use for Informix 4GL report and form creation
• EGL – IBM's EGL MVC Implementation

Perl

• Catalyst An MVC-based avant-garde web framework.

PHP

• Akelos PHP Framework a Ruby on Rails port to PHP4/5.
• barebonesmvc A one-file, no-configuration, PHP 5 MVC framework.
• CakePHP webapplication framework modeled after the concepts of Ruby on Rails.
• CodeIgniter A PHP MVC framework.
• ash.MVC A Simple MVC Framework with PHP.
• FUSE A powerful but easy-to-use PHP 5 Framework for MVC development modeled after the concepts of Ruby on Rails.
• Jelix Framework an open source PHP 5 MVC framework designed for highly performance.
• Joomla v1.5.x is an open source Content Management System that employs the MVC model for its extensions, called components and modules.
• KohanaPHP A powerful, lightweight, easily extendable PHP 5 MVC Framework.
• Konstrukt A PHP MVC / RESTful framework
• LightVC Lightweight PHP 5 Strict MVC Framework with decoupling of Model and other non-View-Controller essentials to promote code reuse.
• Odin Assemble Small footprint PHP based MVC Framework.
• Orinoco Framework is a full-stack yet lightweight framework written in PHP5. It implements the Model 2 design paradigm.
• phpXCore A MVC design pattern based PHP content management framework compatible with PHP4 and PHP5.
• PRADO A PHP 5 MVC framework.
• 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. Much like Ruby on Rails.
• Solar
• Switch board (framework) with Routing PHP 5 MVC Framework with Routing.
• Symfony Framework PHP 5 MVC Framework modeled after the concepts of Ruby on Rails.
• XPT Framework A PHP 5 MVC framework.
• Zend Framework A PHP 5-based MVC framework modeled after the concepts of Ruby on Rails.
• ZNF PHP5 MVC framework for enterprise web applications
• Zoop Framework A Mature PHP 4/5 MVC framework.

Python

• Django A complete Python web application framework. Django prefers to call its MVC implementation MTV, for Model-Template-View.
• Pylons - Python Web Framework
• TurboGears for Python
• web2py Web Framework
• Zope Content Management Framework

Ruby

• Camping
• Merb
• Nitro
• Ramaze
• Ruby on Rails

Smalltalk

• AIDA/Web

XML

• XForms

See also

• Trygve Reenskaug - first formulated the model-view-controller pattern
• Architectural patterns
• Model View Presenter
• Model 1
• Three-tier (computing)
• The Observer design pattern
• The Template Method design pattern
• The Presentation-abstraction-control (PAC) pattern
• The naked objects pattern, often positioned as the antithesis of MVC, though Reenskaug suggests otherwise
• Model View Adapter

References

External links

General information regarding MVC

• An overview of the MVC pattern in Java from the Sun website
• Model View Presenter with ASP.NET CodeProject article.
• History of the evolution of MVC and derivatives by Martin Fowler.
• MVC Framework with PHP
• ASP.NET MVC Framework Microsoft's Scott Guthrie on .NET MVC
• Introduction to the ASP.NET Model View Controller (MVC) Framework Scott Hanselman builds an application step-by-step using the first CTP of the ASP.NET MVC Framework in this Introductory Video
• Greer, Derek. "Interactive Application Architecture Patterns", Ctrl-Shift-B, 2007.

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