Reference stage OOP

[Guest]

from my documentclass  i got a isntance of the my view class in there i got a instance of navigation class extends Sprite

I got a utilz.as file with all static public functions like this one

alignToCenter(obj:DisplayObject):vid

{

     obj.x = obj.stage.stageWidth/2;

}

Utilz.alignToCenter(instance of navigation class)

I get a error stage is null reference..

What is a easy way to fix that?

[Guest]

If i want to create a ViewModel class

and it should have a stage reference

like

package mvc.view
{
    import flash.display.Stage;

    public class ViewModel extends Sprite
    {
        private var s:Stage = new Stage() <--- btu this is really the current stage
       
        public function ViewModel()
        {
           
        }
       
        public function update():void
        {
           
        }       
    }
}

This would be one idea right?

[Muzak]

A DisplayObject's stage property becomes available when the instance is added to the display list.

When trying to access the stage property too soon, it'll throw an error.

Try listening for the ADDED_TO_STAGE event in you custom class, at which time the stage property will be available for use.

[margotdarby]

Yes, null reference error almost always means the thing's not loaded yet. Adding an event listener is the most direct solution. I usually find it easiest just to eliminate any stage-positioning reference that isn't in the main class.

[Guest]

in my main class before i do anything i do :

  public function Main()
        {

addEventListener(Event.ADDED_TO_STAGE, onAddedToStage);
           
            function onAddedToStage(e:Event):void
            {
                removeEventListener(Event.ADDED_TO_STAGE, onAddedToStage);
                stage.scaleMode = StageScaleMode.NO_SCALE;
                stage.align = "TL";
                trace(stage.stageWidth);
                init();    

            }

}

why i get 0 on my trace? stage is there

[kglad · Accepted solution]

Main is your document class?

(and don't nest named functions.)

[Guest]

Yeah!

[margotdarby]

I am pretty sure this is what is going on:

1) Your main/document class brings in another class--called either Navigation.as or Utilz.as (I can't tell), and inside this other class you are centering an object within that class's own stage.

2) But your Utilz.as (or Navigation) class, including all the subclasses and objects inside it, is not fully loaded yet when the Flash engine tries to center an object...

3) So Flash gives a null reference error!

4) Your event listener appears to be in your main class, but your problem is in your utilz or navigation class, and that's where you have to put your listener. If you are going to center an object within a subclass, you have to make sure it is loaded first.

Finally: Try commenting out // that stage-centering property and see if you get a different result.