Mark Ledford’s Blog

[...] Very clear description is here. [...]

It’s not a bug in the Flash architecture, it’s a mistake on the part of the developer. AS3 is different than AS1. In AS3, things that have access to stage are not on stage unless you put them there using addChild. This is not a bug, but a developer mistake.

That being said, most AS3 component authors have proven themselves to be sloppy coders because they release broken components (and charge for them) because they mistakenly assume stage will not be null in the constructor and do not use addEventListener(Event.ADDED_TO_STAGE, onAddedToStage) which is simply good coding practice in AS3. I learned this the very first day I learned AS3, but then again, I read a book about it and didn’t just dive in expecting everything to be the same as AS1.

The solution is simple:

if (stage == null)
{
addEventListener(Event.ADDED_TO_STAGE, onAddedToStage);
}
else
{
onAddedToStage();
}
private function onAddedToStage(event:Event = null):void
{
// init code that requires stage
}

Hi Steve,
Thats why I said I would “kind of” consider it a bug. In the example I’ve included the Loader IS added to the stage before the call to download the SWF. As far as the developer is concerned the SWF has been added correctly beforehand. This is unexpected behavior with how SWFs loaded into SWFs are instantiated.

Something I’m working on currently involves users being able to specify their own swfs to load. A good portion aren’t working because of this issue. Its just annoying that the authors of those swfs have to have the foresight to take the extra step of making their swf compatible. You can’t expect every swf author to do this or follow this “good coding practice” especially if their swf was never originally intended to be loaded into another swf.

I’d actually prefer if “stage” was never accessible by a class constructor so that this “best practice” could be a requirement.

it helped me…as I was also facing the same problem.
I still further get few security errors that is surely solvable but besides that I get an error for stage access as well.
Lets say “swf_contain” is my container swf and “swf_loaded” is my swf being loaded into it.

Now I get error saying:
caller “swf_loaded” cannot access Stage owned by “swf_contain”
at flash.display::Stage/set align()
at net.slideshare.controller::Controller/onAddedToStage()
at flash.display::DisplayObjectContainer/addChild()
at egoWidgetNEW_fla::MainTimeline/playerLoaded()

I just wanted to understand how flash distinguishes between stage of container and loader swf. because here further loading I want it to access stage of loader swf.

Any help would be appreciated. Kindly mail me:)

Hi Sugandha,
Your probably loading a swf from a different domain into the first swf. The flash security sandbox prevents cross domain swfs from accessing each others properties unless explicitly allowed through the code. Try adding this to “swf_contain” and it should work:

Security.allowDomain(”*”);

Regarding how flash distinguishes between the stage of the container and the loaded swf, they reference the same object.

All stage properties references the single base-container Stage instance that all SWFs, including your main SWF and nested loaded swfs are contained in. The “stage” property will be “owned” by your main swf so you need to explicitly allow access to it like any other property of the swf using the above.

There is a nice hierarchy chart here:
http://livedocs.adobe.com/flash/9.0/main/wwhelp/wwhimpl/common/html/wwhelp.htm?context=LiveDocs_Parts&file=00000142.html

thanks so much!

Hi,
I have used above code and when I trace the satge its giving as null but from else code the function is not getting triggered on that addEventListener(Event.ADDED_TO_STAGE, onAddedToStage); event…
donno why? even I cant trace anything in that function..Can any one tell me what Im doing wrong?
thanks in advance

Hi Suresh,
Perhaps that function isn’t your class constructor. Can you paste the code?

You guys are the best. Thanks for the code. bBen searching the net for over 3 hours. Am referring to the topic (swf into swf) in as3. its been bugging sine last night. Your code worked perfectly. Am uploading my new web site in 20 mins. Thanks alot and have a nice day.

[...] Why does my swf work standalone, but when I try and load it into another swf, I get a null object error? Stages. [...]

Hi,
Thanks for the code it helped me a lot, but i try to use this code inside an child swf which have resize and possition function. Everything is working good until i try to resize the swf…I think somethig is wrong with the “possition” function..Bellow i paste my code:

if (stage){
onAddedToStage();

} else {
addEventListener(Event.ADDED_TO_STAGE, onAddedToStage);
}

function onAddedToStage(evt:Event=null):void {
removeEventListener(Event.ADDED_TO_STAGE, onAddedToStage);
stage.align = StageAlign.TOP_LEFT;
stage.scaleMode = StageScaleMode.NO_SCALE;

possitionBar();
stage.addEventListener(Event.RESIZE,positionAll);

}

function possitionBar():void {
bar_mc.bar_mc.width = stage.stageWidth-20;
buttons_mc.x =(stage.stageWidth - buttons_mc.width)/2;

bar_mc.x = 10;
buttons_mc.y = stage.stageHeight - ((bar_mc.height-5 )*2);
bar_mc.y = stage.stageHeight - bar_mc.height;
//positioning the loader
_loader_mc.alpha = .2;
_loader_mc.x = 10;
_loader_mc.y = bar_mc.y;

}

//position all the elements on resize
function positionAll(e:Event):void {

try {
resizeAndPositionTheBigImage(_bigContainer_sp,W ,H,false);

} catch (e:Error) {
}
//positioning the loader
_loader_mc.x = 10;
_loader_mc.y = bar_mc.y;

}

This is the Url:
http://www.fashionbehave.com/SV-project/

Thanks in advance, Flo

Thanks SO much for this code. I have been looking for an answer for this error in clear understandable terms. I am a designer learning how to code. I had several event listeners on the stage and that was the source of the error code.