Flash / ActionScript - application design question

Question

Could someone share the way how this should be designed:

Let's say I have some data model, which is built using Entries.

Basically, I have one abstract class Entry (or interface IEntry - that's not so important for the case) and have several implementations of this class - MovieEntry, SoundEntry, FoodEntry, whatever...

Each of those is a wrapper for some data (url, description, number of calories, etc) and this data is grouped together in each corresponding class.

---

Now - if I wish to display the data for the entries on the screen (let's say movie posters and annotations for the MovieEntry) - how should I design that?

Obviously I could provide another interface / abstract class and call it DrawableEntry (and it would inherit Sprite) and then build a bunch of classes like DrawableMovieEntry and DrawableSoundEntry which could look like:

class DrawableMovieEntry extends DrawableEntry { // which also extends 'Sprite'

   private movieEntry:MovieEntry;

   public override function draw(backend:*) {
      // Draw everything using the 'movieEntry' reference
      // stored.
};

But this seems to be kind of an overkill for a small application.

Another approach is to make the MovieEntry, SoundEntry, ... extend sprite and provide the drawing implementations themselves - but this is obviously bad, because data becomes strongly coupled with it's visualization routines.

So - how should this be done? Maybe MVC approach has something to offer for this case?

Answer 1

Your use case seems to be the perfect example for the Strategy pattern or the Command pattern.
Strategy being the simpler one, here is an example:

Create an IDrawStrategy interface like this:

package {
  public interface IDrawStrategy {
    function draw( obj:Object ) : void;
  }
}

Implement several DrawStrategies:

package {
  public class SoundEntryDrawStrategy implements IDrawStrategy {
    public function draw (obj:Object) : void {
       // cast obj to SoundEntry and do all the drawing necessary, 
       // or fail if obj is null or not a SoundEntry
    }
  }
}

package {
  public class MovieEntryDrawStrategy implements IDrawStrategy {
    public function draw (obj:Object) : void {
       // cast obj to MovieEntry and do all the drawing necessary
       // or fail if obj is null or not a MovieEntry
    }
  }
}

etc.

Then add a new member to your base Entry class:

private var _drawStrategy:IDrawStrategy;

and create a setter:

public function set drawStrategy ( strat:IDrawStrategy ) : void {
    _drawStrategy = strat;
}

and a draw method:

public function draw () : void {
  _drawStrategy.draw( this );
}

You can now assign and execute the fitting strategies to each of your entries:

var mov:MovieEntry = new MovieEntry();
mov.drawStrategy = new MovieEntryDrawStrategy();
mov.draw();

BTW the Sprite you draw the information in can, but doesn't have to, be a member of the DrawStrategy class, but if you wanted to add a clear() method later, it would be better to keep a reference ;).