Program Flow and Event Listeners in ActionScript - actionscript-3

Question

I'm having difficulty with program flow control when XML loads from an external source. I'm using Flash Builder 4.6
What should happen: use a loader. Listen for when it is loaded. When it fires the COMPLETE event, proceed.
What is happening: use a loader. Listen for when it is loaded. But before the COMPLETE event fires, program control returns to the calling class. So meanwhile, the program keeps going and throws an error because it is trying to access data which is null.
Three classes are involved:
AdvocacyWiz.mxml - the base MXML file for this AIR mobile app
Model.as - the model class
myXMLLoader.as - class in which the loader loads data, then
dispatches event when it's done.
I am calling a function setUpModel() in AdvocacyWiz.mxml once AdvocacyWiz.mxml is added to the stage. The setUpModel function in that class just looks like this:
Model.Instance.initialize(); //model is a singleton
The initialize function call invokes a loader in my XMLLoader.as class. That's where the event listener is left listening for the Complete event, which happens too late to prevent a null error from occurring.
EDIT: Here's the code --
In AdvocacyWiz.mxml (this fires first):
protected function addedToStageHandler(event:Event):void
{
setUpModel();
stage.scaleMode = StageScaleMode.NO_SCALE;
//... additional layout functions
private function setUpModel():void {
Model.Instance.initialize();
}
In Model (this fires second):
public function initialize():void {
addEventListeners(); //this includes listener for StoriesXMLLoader.STORY_LOADED event which will be dispatched from the loader class.
useExternalXML();
...
}
private function useExternalXML():void
{
myLoader.getStory("1140");
}
In the Loader class:
public function getStory(storyId:String):void {
var url:String = "http://mysite.com/whatever.xml";
myLoader.dataFormat = URLLoaderDataFormat.TEXT;
myLoader.addEventListener(Event.COMPLETE, storyXMLLoaded);
myLoader.load(new URLRequest(url));
}
private function storyXMLLoaded(e:Event):void {
storyXML = new XML(e.target.data);
dispatchEvent(new Event(StoriesXMLLoader.STORY_LOADED));
}
What I want to do is call setUpModel() but not have flow returned to the mxml class until the model actually has data.
Thanks.

Answer 1

Well, you haven't provided any code, which would help considerably, but here's a few pointers.
What should happen: use a loader. Listen for when it is loaded. When
it fires the COMPLETE event, proceed. What is happening: use a loader.
Listen for when it is loaded. But before the COMPLETE event fires,
program control returns to the calling class. So meanwhile, the
program keeps going and throws an error because it is trying to access
data which is null.
A lot of Flex is asynchronous. What this means is that when you try to load from the external source, program control immediately returns, as you noted.
In order to have the kind of program flow you want, you need to have the function that calls load() end after that call. Then, when the COMPLETE event listener fires, you can execute the remainder of the code that causes the null exception.