About scope in classes

When you port code to ActionScript 2.0 classes, you might have to change how you use the this keyword. For example, if you have a class method that uses a callback function (such as the LoadVars class's onLoad method), it can be difficult to know if the this keyword refers to the class or to the LoadVars object. In this situation, you might need to create a pointer to the current class, as the following example shows:

class Product {
    private var m_products_xml:XML;
    // Constructor
    // targetXmlStr contains the path to an XML file
    function Product(targetXmlStr:String) {
        /* Create a local reference to the current class. 
            Even if you are within the XML's onLoad event handler, you 
            can reference the current class instead of only the XML packet. */
        var thisObj:Product = this;
        // Create a local variable, which is used to load the XML file.
        var prodXml:XML = new XML();
        prodXml.ignoreWhite = true;
        prodXml.onLoad = function(success:Boolean) {
            if (success) {
                /* If the XML successfully loads and parses, 
                    set the class's m_products_xml variable to the parsed 
                    XML document and call the init function. */
                thisObj.m_products_xml = this;
                thisObj.init();
            } else {
                /* There was an error loading the XML file. */
                trace("error loading XML");
            }
        };
        // Begin loading the XML document
        prodXml.load(targetXmlStr);
    }
    public function init():Void {
        // Display the XML packet
        trace(this.m_products_xml);
    }
}

Because you are trying to reference the private member variable within an onLoad handler, the this keyword actually refers to the prodXml instance and not to the Product class, which you might expect. For this reason, you must create a pointer to the local class file so that you can directly reference the class from the onLoad handler.