cristobal baray
kids iPhone apps
s100+ pages

Last edited - March / 99
-- Hear and forget; see and remember; do and understand...

the model-view-controller (MVC) design pattern

introhereexample appmodelscontrollersviewstodosrefs

MVC advantages

Just by breaking the program down into the three MVC components, one gains many advantages. These are the most significant ones I've found through my own experience:

  • Clarity of design : the public methods in the model stand as an API for all the commands available to manipulate its data and state. By glancing at the model's public method list, it should be easy to understand how to control the model's behavior. When designing the application, this trait makes the entire program easier to implement and maintain.
  • Efficient modularity of the design allows any of the components to be swapped in and out as the user or programmer desires - even the model! Changes to one aspect of the program aren't coupled to other aspects, eliminating many nasty debugging situations. Also, development of the various components can progress in parallel, once the interface between the components is clearly defined.
  • Multiple views : the application can display the state of the model in a variety of ways, and create/design them in a scalable, modular way. This comes up in games, with a cockpit and a radar view, and in my research applications, where I have a view to display the state of the model and another view that collects data, calculates statistics, then to saves the data to disk. Both views are using the same data, they just use the information differently. During the development process, I usually start out with a text based view, which just prints out the data that the model is generating. Later, as I create new views, I can use the text based view to verify the performance of the new views.
  • Ease of growth : controllers and views can grow as the model grows; and older versions of the views and controllers can still be used as long as a common interface is maintained (the text view just mentioned is an example). For instance, if an application needs two types of users, regular and administrator, they could use the same model, but just have different controller and view implementations. This is related to the similarity with the client/server architecture - where the new views and servers are analogous to the clients.
  • Distributable : with a couple of proxies (another design pattern - used in the snake game) one can easily distribute any MVC application by only altering the startup method of the application. Now, the application becomes a full fledged set of client and server applications.
  • Powerful user interfaces : using the model's API, the user interface can combine the method calls when presenting commands to the user. Macros can be seen as a series of "standard" commands sent to the model, all triggered by a single user action. This allows the program to present the user with a cleaner, friendlier interface.

Now, let's see how this is really applied...

introhereexample appmodelscontrollersviewstodosrefs