[RESOLVED] Referencing Stage within custom "Global" class

[badaboom55]

Hello All,

I'm new to OOP and I still haven't gotten a handle on coding classes and the appropriate syntax with all the "public" "private" "static" keywords, etc.
Anyway, one thing I miss in AS3.0 is having "out-of-the-box" global variables and functions.
I've read a lot of forums and articles about making a simple "MyGlobal" class that could hold variables and functions which could be called from the timeline as "MyGlobal.doSomething()"
However, I seem to be running into a problem trying to reference "stage" from within one of the global functions... I imagine this is because "stage" is an instance property.
I'm basically trying to add/remove an event listener to the stage whenever the global function "MyFunction" is called.

MyGlobal.as:

package{
    
    import flash.display.*;
    import flash.events.KeyboardEvent;
    
    public class MyGlobal{
        
        public static var objVars:Object = new Object();

        public static function MyFunction(Previous_mc:MovieClip, Target_mc:MovieClip):void{
            // Remove the previous keyboard listener
            stage.removeEventListener(KeyboardEvent.KEY_DOWN, Previous_mc.fOnKeyDown, false);
            // Add a keyboard listener that targets the Target_mc's fOnKeyDown function
            stage.addEventListener(KeyboardEvent.KEY_DOWN, Target_mc.fOnKeyDown, false, 0, true);        
        }
        
    }
    
} 

MyApplication.fla Timeline:

MyGlobal.objVars.myVar1 = "Hello World";
trace(MyGlobal.objVars.myVar1); // output: Hello World

MyGlobal.MyFunction(myMC1_mc, myMC2_mc); 

Compiler Error:

1120: Access of undefined property stage.

Am I missing an import statment, or is there someway I need to declare stage as this.stage?

[Baby Minion]

http://help.adobe.com/en_US/AS3LCR/F...ect.html#stage

The stage property is only accessible by DisplayObject that are in a display list, or the main class, or timeline.

What I suggest, is making a variable in your MyGlobal class called stageRef. At the beginning of your application, set the stageRef = stage. Then all of your functions that require a reference to the stage will be able to access it through the stageRef class.

package{
    
    import flash.display.*;
    import flash.events.KeyboardEvent;
    
    public class MyGlobal{
        
        // added stage ref
        public static var stageRef:Stage;
        public static var objVars:Object = new Object();

        public static function MyFunction(Previous_mc:MovieClip, Target_mc:MovieClip):void{
            // Remove the previous keyboard listener
            stageRef.removeEventListener(KeyboardEvent.KEY_DOWN, Previous_mc.fOnKeyDown, false);
            // Add a keyboard listener that targets the Target_mc's fOnKeyDown function
            stageRef.addEventListener(KeyboardEvent.KEY_DOWN, Target_mc.fOnKeyDown, false, 0, true);        
        }
    } 
} 

[badaboom55]

So, I would just have to add "MyGlobal.stageRef = this.stage;" to my timeline code, like so:

MyGlobal.stageRef = this.stage;

MyGlobal.objVars.myVar1 = "Hello World";
trace(MyGlobal.objVars.myVar1); // output: Hello World

MyGlobal.MyFunction(myMC1_mc, myMC2_mc); 

Is there anyway to declare the stageRef within the MyGlobal class .as file itself? Instead of having to define stageRef at runtime via frame actions?

I suppose I understand that I'm not adding an instance of the MyGlobal class to the display list, so maybe I've answered my own question... it's not a deal-breaker either way.
Writing "MyGlobal.stageRef = stage" at the beginning of every application isn't much of an inconveinence... but it would be nice if MyGlobal could just do it automatically by grabbing the "this.stage" of wherever "MyGlobal.something()" is being called... since MyGlobal will only be called by either 1) other class instances (MovieClips, Buttons, etc.) already existing in the Display List, or 2) by the actions on the root timeline (as above).

[5TonsOfFlax]

Baby Minion's solution will work, but why do you need that in a global scope anyway? It seems more like something that should go in the document class.

[badaboom55]

If you can explain briefly...
Why/What are you suggesting should go in the document class? What are the benefits of the document class vs. what I'm trying to do?

Reading a bit, I see that "the document class serves as a shortcut for creating an instance of a MovieClip or Sprite and adding it to the display list..."
Does this mean if I use a document class, I don't have to declare stageRef = stage from the timeline?

I'm not sure I need anything in the "global scope" as you put it... it's just what I was used to in AS2.0, because you could declare a function or variable as global by using "_global"... so usually I would just define my global stuff on Frame 1 of the Main Timeline
So in attempting to transition over to AS3.0, I did a few searches on "AS3 global functions and variables". And the common solution was a custom class.

To my thinking... I want variables within the global scope so that I don't have to write (using AS2.0 timeline coding logic):

MovieClip(parent.parent.parent.parent.parent.parent).myVar1 = "Hello"; 

Similarly, if I have a function that isn't necessarily project specific... such as a function that converts us dollars to bhutanese money... I don't want to have to write:

MovieClip(parent.parent.parent.parent.parent.parent).fConvertUSDtoBHU(263.00); 

Now, if I had several common functions, I don't think I'd necessarily want a ".as" file for each... so why not bundle them into 1 ".as" file which I can just reference as needed from ANY .fla:

myGlobal.fConvertUSDtoBHU(263.00); 

If it's flawed logic, I'd love to hear why, or how anybody would handle a set of functions which may or MAY NOT be needed in any given project?

[5TonsOfFlax]

Definitely do not use parent.parent.parent etc. At the very least keep a reference to the instance with the var or function you need.

The document class is the class which will be associated with the root. Properties and functions defined I'm the document class will be available in the main timeline, and by calling them with the root reference (after casting).

What you have described with the convert function is a static utility class. There's nothing wrong with those, but try to keep them stateless.

[badaboom55]

The document class is the class which will be associated with the root. Properties and functions defined I'm the document class will be available in the main timeline, and by calling them with the root reference (after casting).

So do you mean by using a document class, I could call a function within the document class like this?

MovieClip(root).myDocClassFunction(); 

Why is that better than this:

myGlobal.myGlobalClassFunction(); 

What you have described with the convert function is a static utility class. There's nothing wrong with those, but try to keep them stateless.

What do you mean by stateless?

Sorry, I know this is a forum, not a classroom.

[5TonsOfFlax]

Within the document class or the main timeline (which IS the root), you could just do:

myDocClassFunction();

From other instances/classes you would still need to get a reference to the document instance to call that function.


By stateless, I mean that it does not keep any info around in variables between function calls. It should not have any modes set or things like that. This is not required, it's just good practice. If you do need state, then the class should not be static, you should get an instance to store in whatever scope you need it.

The reason to avoid storing state in a static class is that other stuff you might not plan on could alter that state. Say your convert utility was written in a stateful manner, where you'd have to set the to-unit and the from-unit, then call convert. Between calls to convert, another class might change the units, and mess up your values. If instead, you had function convert(from, to, value):Number, then each call would be completely independent of anything else that has happened to the class.