Thanks for that link! I didn’t realize Cocoa was designed around the MVC.

Kindest regards,
Bill

Good question. I’d have to begin with the main query, “What varies?”. I believe that the Observer pattern would be most useful because different objects (analog and digital compass displays) depend on the information from the object that generates the information.

What do you think?

Kindest regards,
Bill

Great article! Your writing is clear and makes it easy to understand.

If you had to redo the compass example in a way you prefer what would that be? Hopefully you can do your next blog on that.

Thank you,
~mark

First of all, Chandima is the real MVC expert here—both MVC and PureMVC. Your questions are all handled better in Chapter 12 than I could in a short note to you. (Also, Chandima could do it better.)

Second, I’m not that enthusiastic about the MVC. GoF make reference to it almost in passing in Chapter 1 of their book, and it is not actually a design pattern so much as it is a heuristic device for helping to understand design patterns. Somehow, it has become the favorite framework for many developers, and so I thought it wouldn’t hurt to look at it and use it as an example of structure. That was what the bridge was for—illustrating different structures.

The best place to start with the MVC or any other design pattern is to ask:

What varies?

Once that question is addressed, you can then select the design pattern that handles variation. So instead of beginning by asking How do I handle this problem? you need to back away and look at the principles on which design patterns are based.

All of the tools you need for this are pulled together in a Starter Kit on this blog. That will put you on the right path.

Kindest regards,
Bill

Wow! I’m so glad I came across this huge article! I have looked at the surface of MVC for a while now without truly understanding the flow of communication between the segments of code (Model, View and Controller). I now feel enlightened and can’t wait to begin tackling my new applications with this design pattern.

I didn’t quite get the bridge bit about the bridge not being able to stand up with square supports and why it would fall sideways. However I did understand what you meant about solid non-substandard structure code-wise.

Now I do have one particular question. I am working on a Drupal Flash website and I have pretty much written the code for it to work. However, I have all written it in a class called “Interface.as”, i.e. non-MVC. In your example you seperated some pretty simple code into M, V and C with a client to instantiate, but in my application/website as3 code there are various “modules” (if I can call them that) due to the fact that a website doesn’t contain only a compass needle and a slider. It contains more things such as “language selection”, “web pages”, “product photo gallery”, “news”, “menu” etc. Also it contains main site information that remains pretty much constant throughout the site like a variable such as “_siteDomain”. What I can’t seem to get my head around is:

Where do I start?
How do I separate the “modules” and how do they communicate with each other?
How would I go about planning the MVC?
What kind of tools are there to conceptualize an application specific to as3?

Thank you very much for having taken the time to write such an in depth and enlightening article and if you do find the time to answer my questions I would like to thank you in advance.

Best Regards,
Alexandre

The point of this particular post is code re-use and the simple (and trivial) example is to show how easy it is to use the bulk of the code with a different view. So, it’s really about re-use, and I was hoping the comments might reflect that.

The MVC is a fairly flexible framework, and I’d really like to see you take my example and fix it up with your registration process with a different view. Let’s see what you got.

Kindest regards,
Bill