The MVC definition has been abused

Summary

Smalltalk MVC is defined in Design Pattern as: MVC Consists of three kinds of objects. The Model is the application object, the View is its screen presentation, and the Controller defines the way the user interface reacts to user input. However this definition has been abused over the years - Back in 2003 I gave a talk citing how bad Apple’s definition was. At the time it stated: A view object knows how to display and possibly edit data from the application’s model… A controller object acts as the intermediary between the application’s view objects and its model objects… Controllers are often the least reusable objects in an application, but that’s acceptable… Of course it isn’t acceptable and, over the years, Apple has refined their definition and now acknowledge the distinction between the traditional Smalltalk version of MVC and the Cocoa version. But the Cocoa version is still defined much as it was before: A view object knows how to display, and might allow users to edit, the data from the application’s model… A controller object acts as the intermediary between the application’s view objects and its model objects… In looking at how iOS applications are written the sentiment that controllers (and now view-controllers) are often the least reusable components in an application still flourishes, even if it is now unstated. MVC (I’ll always use that term to refer to the Smalltalk form) has the following structure: figure: Smalltalk MVC Here the solid lines imply a direct association. And the dashed lines an indirect association by an observer. So what we see is that the model is unaware of the view and controller, except indirectly through notifications, and hence the code in the Model is reusable. The controller and view bind to the model, not the other way around. Often the function of the Controller and View are tightly coupled into a “widget” or “control”. When Apple talks about a View-Controller in their model they are talking about a grab-bag of an uber-widge...