Model–view–controller

Model–view–controller (MVC) is a software design pattern for implementing user interfaces on computers. It divides a given software application into three interconnected parts, so as to separate internal representations of information from the ways that information is presented to or accepted from the user.^[1][2]

Traditionally used for desktop graphical user interfaces (GUIs), this architecture has become popular for designing web applications and even mobile, desktop and other clients.^[3]

Description

As with other software architectures, MVC expresses the "core of the solution" to a problem while allowing it to be adapted for each system.^[4] Particular MVC architectures can vary significantly from the traditional description here.^[5]

Components

A typical collaboration of the MVC components.

The central component of MVC, the model, captures the behavior of the application in terms of its problem domain, independent of the user interface.^[6]

• The model directly manages the data, logic, and rules of the application.
• A view can be any output representation of information, such as a chart or a diagram. Multiple views of the same information are possible, such as a bar chart for management and a tabular view for accountants.
• The third part, the controller, accepts input and converts it to commands for the model or view.^[7]

Interactions

In addition to dividing the application into three kinds of components, the model–view–controller design defines the interactions between them.^[8]

• A model stores data that is retrieved according to commands from the controller and displayed in the view.
• A view generates new output to the user based on changes in the model.
• A controller can send commands to the model to update the model's state (e.g., editing a document). It can also send commands to its associated view to change the view's presentation of the model (e.g., by scrolling through a document).

History

One of the seminal insights in the early development of graphical user interfaces, MVC became one of the first approaches to describe and implement software constructs in terms of their responsibilities.^[9]

Trygve Reenskaug introduced MVC into Smalltalk-76 while visiting the Xerox Palo Alto Research Center (PARC)^[10][11] in the 1970s. In the 1980s, Jim Althoff and others implemented a version of MVC for the Smalltalk-80 class library. Only later did a 1988 article in The Journal of Object Technology (JOT) express MVC as a general concept.^[12]

The MVC pattern has subsequently evolved,^[13] giving rise to variants such as hierarchical model–view–controller (HMVC), model–view–adapter (MVA), model–view–presenter (MVP), model–view–viewmodel (MVVM), and others that adapted MVC to different contexts.

The use of the MVC pattern in web applications exploded in popularity after the introduction of Apple's WebObjects in 1996, which was originally written in Objective-C (that borrowed heavily from Smalltalk) and helped enforce MVC principles. Later, the MVC pattern became popular with Java developers when WebObjects was ported to Java. Later frameworks for Java, such as Spring (released in 2002), continued the strong bond between Java and MVC. The introduction of the frameworks Rails (December 2005, for Ruby) and Django (July 2005, for Python), both of which had a strong emphasis on rapid deployment, increased MVC's popularity outside the traditional enterprise environment in which it has long been popular. MVC web frameworks now hold large market-shares relative to non-MVC web toolkits.^[14]

Use in web applications

Although originally developed for desktop computing, model–view–controller has been widely adopted as an architecture for World Wide Web applications in major programming languages. Several commercial and noncommercial web frameworks have been created that enforce the pattern. These software frameworks vary in their interpretations, mainly in the way that the MVC responsibilities are divided between the client and server.^[15]

Early web MVC frameworks took a thin client approach that placed almost the entire model, view and controller logic on the server. This is still reflected in popular frameworks such as Ruby on Rails, Django, ASP.NET MVC. In this approach, the client sends either hyperlink requests or form input to the controller and then receives a complete and updated web page (or other document) from the view; the model exists entirely on the server.^[15] As client technologies have matured, frameworks such as AngularJS, EmberJS, JavaScriptMVC and Backbone have been created that allow the MVC components to execute partly on the client (also see Ajax).

See also

• Hierarchical model–view–controller
• Model–view–adapter
• Model–view–presenter
• Model–view–viewmodel
• Naked objects
• Observer pattern
• Presentation–abstraction–control

References

Bibliography

Wikibooks has a book on the topic of: Computer Science Design Patterns/Model–view–controller

External links

• What Are The Benefits of MVC? – quotes at length from the Gang of Four
• Martin Fowler on the history of UI Architectures and the evolution of MVC
• Understanding MVC architecture – a quick explanation on YouTube
• 1. MVC and Introduction to Objective-C (September 27, 2011). Stanford University introductory lecture on the MVC pattern. on YouTube
• Cocoa Core Competencies: Overview of the MVC pattern.