Question

I’ve been having a problem that’s plagued me many times in the course of developing a Flash project. It looks something like this:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at fl.containers::BaseScrollPane/fl.containers:BaseScrollPane::drawBackground()
at fl.controls::TileList/fl.controls:TileList::draw()
at fl.core::UIComponent/::callLaterDispatcher()
TypeError: Error #2007: Parameter child must be non-null.
at flash.display::DisplayObjectContainer/addChildAt()
at fl.controls::BaseButton/fl.controls:BaseButton::drawBackground()
at fl.controls::BaseButton/fl.controls:BaseButton::draw()
at fl.core::UIComponent/drawNow()
at fl.controls::ScrollBar/fl.controls:ScrollBar::draw()
at fl.core::UIComponent/::callLaterDispatcher() 

Now, in my case, this error stems from initializing components in code when they have not been explicitly added to the fla’s component library in CS4. In the past, I have run into this issue when trying to dynamically create ScrollPanes in code. I have solved it by adding ScrollPane components to my Main.fla’s library. This seemed to work for a while.

Now, I am trying to use an AstraFlash AutoComplete box. I have imported the proper fla files into CS4, and placed an AutoComplete box into my Swf. Everything builds fine, but the above error occurs when the Swf is loaded. My thought is that the AutoComplete box is trying to create a ScrollPane as part of its functionality. Ok, I understand this, so I add the ScrollPane component to the library as well with the same results.

Usually I would just mess with the library components/settings until I get rid of the error, but I’m sick of running into this, and I want to know the correct way to solve the problem. So, here are a few questions I have:

• When are you required to add a component to a Fla’s library rather than just creating the component in code?

• Which Flas do you need to add the component to? Just the one using it? Or all of parents of that Fla as well?

• Let’s say the Autocomplete component requires a ScrollPane component. Why isn’t this dependency recognized when I add the one component? Why must I explicitly add it?

• What is the difference between adding a component to the library, and adding it to the library’s ‘Component Assets’ folder? What is this folder’s purpose?

I really need this AutoComplete component to work. Assuming the AS3 code is correct, and I am still getting the above error, what settings do you think are probably incorrect? Out of frustration, I have tried adding every possible component to the library, as well as to the library’s component assets folder just to have a starting point, but I still get the error.

Any help is appreciated.

Answer 1

I’m not sure I understand you’re setup. What I’m assuming is you have a child fla that contains some components and you need to create instances of those components in a parent(loader) fla.

It should work if you compile the classes from the child fla into the parent fla, but that would duplicate things.

The issue is when you load a swf, the classes sit in a different ApplicationDomain.
Simply put, that’s the thing that manages classes in a swf so you don’t have class collisions between a loader and loaded swf and some other security stuff.

I made a simple fla that holds a Button component(fl.controls.Button) and loaded that from a loader fla. I didn’t add the Button component to the loader fla, but did create a button instance, using the loaded swf’s application domain. Here’s how:

var loader:Loader = new Loader();
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, loaded);
loader.load(new URLRequest('componentContainer.swf'));

function loaded(event:Event):void {
   addChild(loader.content);
   var SWFButton:Class = loader.contentLoaderInfo.applicationDomain.getDefinition('fl.controls.Button') as Class;
   var button = new SWFButton();
   button.label = 'Test';
   addChild(button);
}

There is a page in Programming Actionscript 3.0 about thise kind of issues and how to use ApplicationDomain, but I didn’t fully understand it to be honest.

HTH,
George