Need some help getting started with OOD in ActionScript 3

Question

So being new to AS3 but not development in general, during a recent project that I just started I hit an immediate snag where my normal method of OOD is causing errors in AS3.

I created a layer in Adobe Flash called code just to keep everything separate and in frame one under actions I used the following code to get started:

var GameContainerSize:int = 400;

class GameInfo {
    var GameID:int;
    var HomeTeam:String;
    var VisitingTeam:String;
    function GameInfo()
    {

    }
}

This simple code immediately causes an error though

Scene 1, Layer 'Code', Frame 1, Line 4 1131: Classes must not be nested.

And my best guess is this is because the timeline and all code on it exists within a class already. So what should I be doing if I want to develop this program using class objects, or is this even possible in flash?

Answer 1

You can't define classes on the timeline. Each timeline is exported as a class, var and function declarations become members of the class, and frame code is moved to its own frame functions which are called when the timeline reaches that frame. Thus the error is saying "you can't put a class in a class" because the timeline already is a class.

To define classes you must use external .as files with package blocks:

// GameInfo.as
package {
    public class GameInfo {
        public var GameID:int;
        public var HomeTeam:String;
        public var VisitingTeam:String;
        public function GameInfo(){ }
    }
}

In Flash Pro you can link a class to a timeline (document or symbols). Such a class must extend Sprite or MovieClip.

You can also refer to any of your classes from any frame script. For example, you could put on frame 1 of your main timeline:

var gameInfo:GameInfo = new GameInfo();

Typical OOP would involve using external .as class files for almost everything, with only minimal function calls on your timeline frames, like stop() at the end of a timeline or calling a custom function you've added to the class linked to the timeline.

Answer 2

I created a layer

That's not ideal. The problem is that it will not get you any closer to understanding the code, because it isn't code. It's a feature of the flash authoring environment. You might as well spend a day with the drawing tool drawing something.

to keep everything separate and in frame one under actions

Organisation is important, but layers aren't the way to go. As each class definition goes into its own external file, you have to create additional files anyway if you want to create more classes. And you want to create more classes because having only one is horrible object oriented design. Being consistent here is important. That's why people in the comments suggested to use a document class and have no code on any frames. All code is organised in classes. No exceptions¹.

Having said all that, I highly advice against using Adobe Flash to learn As3. There's too much obfuscation going on behind the scenes. If you want to learn how to code As3, use a code editor. (or plain text editor + compiler if you prefer). Learning what settings dialog has to be adjusted in order to get what you want is not going to get you any closer to understanding OOD in As3.

I also see package, is this kind of like a namespace and does it need to be named, if not what is its purpose?

No, packages are packages and namespaces are namespaces. Apples and oranges.

• Packages are used to organize classes just like a structure of folders is used to organize the .as fiels of those classes. In fact, the package is pretty much exactly that folder structure, for example:

  • flash.display is for all display related classes
  • flash.events is for events

• A namespace allows you to control access to members of a class. Namespaces are very rarely used in As3. Here's an article from grant skinner about namespaces. Personally, I never needed to use namespaces. If you are jsut getting started, you can very well ignore them for now.

That sounds perfect! except I cannot get it to launch on my Win10 machine. I may just end up outsourcing this at this ratio

flash develop is the alternative editor. It's free, fast and lightweight.

my normal method of OOD

You want to extend your definition of normal with

• always explicitly specify the access control modifiers

• member names start with small letters

  public class GameInfo {
      private var gameID:int;
      private var homeTeam:String;
      private var visitingTeam:String;
  
      function GameInfo()
      {
  
      }
  }
  

---

¹admittedly, there are top level functions that are pretty much free floating functions without a class. If you want to do oop, this is not what you want. It's for the occasional independent utility function. Stick to classes for now.