Friday, July 30, 2010

Rolling in the mud.

Every idea starts its life as a shiny new marble. Unfortunately the world around us is a pretty muddy place, and when that idea gets pushed around in the real world, it soon starts collecting mud.

Software development has had countless shiny marbles since I started in the industry, and it's pretty interesting watching as they all slowly succumb to the mud. Development languages, best practices, design patterns, frameworks, etc. Each virtually glows with merits and virtues, flinging mud on its predecessors. Everyone wants a turn at pushing around the new shiny marble, but pretty soon it too is coated in mud.

A most recent example: MVVM (Model View View-Model) This is a relatively new design pattern stemming from the MVC (Model View Controller) pattern ancestry. Essentially you have a history that we'll start off at MVC which is a great pattern for earlier, relatively state-expensive terminal applicationa, and is very well suited to stateless web applications. However, for environments where maintaining state was cheap, and users wanted GUI-rich applications, a new shiny variation was born, MVP. (Model View Presenter) It's essentially the same thing, just with some responsibilities shifted between layers. A good explanation can be found here.

Microsoft chased MVP for quite a while with their WinForms and later, WebForms implementations. WebForms was a bit of a disaster because of the cost of maintaining state over the wire.

Martin Fowler coined a new design pattern called Presenter Model which was essentially a MVP pattern where the Presenter was converted into a representation of the model for the view. A subtle variation of this was later given the title of MVVM, and the next shiny marble began rolling around. Microsoft re-defined the way they represent views in both applications and web applications to utilize XAML, pushing aside the older WinForm and WebForm constructs in favour of WPF and Silverlight. These were designed to gel with this new MVVM pattern.

The part I find odd is the seemingly outright vilification of the code-behind aspect still present in XAML, similar to the construct used in WinForms and WebForms. Back in the day these were shiny features, now they're shunned, and to be replaced at all cost with new shiny features.

But it's kind of funny, because in flinging the mud on code-behind, it seems that MVVM is starting to roll deeper into the mud itself. MVP would rely somewhat on code-behind. In a clean example, the code-behind would essentially implement events from the view definition (interface) and upon receiving an event from a UI element such as a button, raise an appropriate view event to the presenter. You might also have some simple method declarations that the presenter can call into the view to perform actions. (Such as clearing out all fields, etc.) The view is essentially anemic. But, there is code-behind.. POO-POO!

In MVVM-land, your view is bound to a View-Model, and your View-Model can define Commands that can bound to things like buttons, so that clicking a button will automatically execute a command. Ok, I can see the merit in this, but wait, it's not that simple, it's got to be shinier. The Command accepts delegates so you can define what the command does.... back in the View-Model.... um, ok... This is starting to smell. Great, so we can put command logic in the View-Model, that is delegated through another object, just so we can avoid declaring an event in code-behind.

Granted, there is some merit in this approach. This does mean that a "designer" can tweak behaviour in an application merely by editing XAML, they don't need to see C#/VB code-behind files. But, they still need to know what these commands are so they can wire them up in a view. In the end, the code is more complicated, with Func<> declarations scattered around and Lambdas, etc. all to remove a couple of simple events.
Now I find this whole argument of defining more stuff in XAML a pretty weak one. How many companies actually advertise for and hire "designers"? More importantly, is it such a huge ask to have a developer work with one of these designers to wire up UI changes, in the event that a designer with a likely web background that has to be able to breathe Javascript, couldn't figure out how to wire an event in C#?

MVVM is starting to get ripe with issues where those wonderful savings that it offered over MVP and code-behind. Setting focus after validation, and dealing with message boxes are just a couple that are popping up. It's not that these issues don't have solutions, but these solutions are typically either hacks around limitations, or fairly complex solutions for what should be simple issues that have been done to death in earlier patterns.

MVVM is getting muddy. I wonder when the next shiny marble will appear.

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