Saturday, October 30, 2010

MVC is not Elegant, It's the Only Thing that Works

I was doing some Swing programming over the summer. Although I've long been familiar with MVC concepts and although I've been doing Swing programming almost since Swing first came out, it was only this summer when I *really* started understanding MVC.

In the past, I always understood MVC in terms of "elegance." Designing UI frameworks using MVC concepts supposedly resulted in a more elegant design. One could easily change the look of a component and reuse behaviours in different widgets. Separation of presentation from data and control logic led to a cleaner design where orthogonal issues would be stored in different places in the code instead of all grouped together.

In fact, this is all wrong. People don't use MVC because it is elegant. People use MVC because for certain user interfaces, MVC is the only design that works. As such, you don't have much choice. If you have a UI design that allows for two views on the same piece of data, you need MVC (for example, if you have two word processing windows open on the same document--so when you type things in one window, these changes should be reflected in the other window as well). Once you need to support this situation in a UI, then MVC just naturally falls out.

  • If you have two windows for editing the same data, you need code to let the user edit data: that's the controller.
  • You need to store the data in one spot (not separately in each window) or else it will get out of sync in the two windows: there's your data model
  • Finally, whenever the data changes, it needs to update both windows to reflect the changes: that's the view

Once you want to support two views of the same piece of data, the reasoning behind MVC becomes obvious. MVC is not elegant. In fact, for simple UIs that only need to support a single view on a piece of data, MVC is unnecessarily complicated. MVC exists because it is the only design that works for complicated UIs. They really should state this outright in documentation instead of rambling on about this elegance nonsense.

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