Model–view–controller

Model–view–controller (MVC) is a software pattern for implementing user interfaces. 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] The central component, the model, consists of application data, business rules, logic, and functions. 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.^[3]

Component interactions

In addition to dividing the application into three kinds of components, the Model–view–controller (MVC) design defines the interactions between them.^[4]

• 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).
• A model notifies its associated views and controllers when there has been a change in its state. This notification allows views to update their presentation, and the controllers to change the available set of commands. In some cases an MVC implementation might instead be "passive," so that other components must poll the model for updates rather than being notified.
• A view is told by the controller all the information it needs for generating an output representation to the user. It can also provide generic mechanisms to inform the controller of user input.

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 all major programming languages. Several commercial and noncommercial application frameworks have been created that enforce the pattern. These frameworks vary in their interpretations, mainly in the way that the MVC responsibilities are divided between the client and server.^[5]

Early web MVC frameworks took a thin client approach that placed almost the entire model, view and controller logic on the server. 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.^[5] As client technologies have matured, frameworks such as JavaScriptMVC and Backbone have been created that allow the MVC components to execute partly on the client (see also AJAX).

History

MVC was one of the seminal insights in the early development of graphical user interfaces, and one of the first approaches to describe and implement software constructs in terms of their responsibilities.^[6]

Trygve Reenskaug introduced MVC into Smalltalk-76 while visiting Xerox Parc^[7][8] in the 1970s. In the 1980s, Jim Althoff and others implemented a version of MVC for the Smalltalk-80 class library. It was only later, in a 1988 article in The Journal of Object Technology, that MVC was expressed as a general concept.^[9]

The MVC pattern has subsequently evolved,^[10] giving rise to variants such as HMVC, MVA, MVP, MVVM, and others that adapted MVC to different contexts.

See also

• Hierarchical model–view–controller
• Model–view–adapter
• Model–view–presenter
• Model View ViewModel
• Observer pattern
• Presentation–abstraction–control
• Three-tier architecture

References

External links

• Model-View-Controller Pattern in WikiBooks.
• What Are The Benefits of MVC? - quotes at length from the Gang of Four (software).
• Martin Fowler on the history of UI Architectures and the evolution of MVC
• YouTube: MVC (Model View Controller) - A quick explanation.
• YouTube: 1. MVC and Introduction to Objective-C (September 27, 2011). Stanford University introductory lecture on the MVC pattern.

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