AS3 - Parametrized Factory method using actual class name

Question

Rather than use a hard-coded switch statement where you pass it the string name of a class and it then instantiates the appropriate class, I'd like to pass the actual name of the class to my factory method and have it dynamically create an instance of that class. I thought it would be trivial and am surprised it is not working. I must be missing something quite basic:

sample code:

createProduct(50, "Product1Class");
createProduct(5, "Product2Class");


private function createProduct(amount:uint, productClassName:String):void {
    var productReference:Class;
    try {
        productReference = getDefinitionByName(productClassName) as Class;

        for (var i:uint = 0; i < amount; i++) {
        var product = new productReference() as ProductBaseClass; // throws reference error!
        }
    } catch (error:ReferenceError) {
        throw new ReferenceError(error.message + " Have you linked a library item to this class?");
    }
 }

The only thing that may be a little odd (not sure) is that these "products" are actually linked Library items (ie: I have a movieClip in the Library that has a linkage to Product1Class and another to Product2Class both of which extend ProductBaseClass, which in turn extends MovieClip.

Why the ReferenceError?

Answer 1

getDefinitionByName() and ApplicationDomain.currentDomain.hasDefinition() require full qualified class names. The example code in the original post works when Product1Class and Product2Class are in the default package. However, if you move the product classes to another package, you have to make sure that you are supplying the fully qualified class name to getDefinitionByName().

So if we put our product classes in com.example.products, then the call becomes:

productReference = getDefinitionByName("com.example.products.Product1Class") as Class;

I'm not really sure what the best practice is with this kind of dynamic factory class, but what I ended up doing (since all products were in the same package) was to create a constant within my factory class that defines the package for my products:

private const PRODUCT_PACKAGE:String = "com.example.products."; // note the trailing period

So that way your client code doesn't need to know (nor define) the product package. You just prepend this constant to your product class name when using getDefinitionByName().

Answer 2

If you have a runtime loaded library then the Class's are not compiled into the main swf, so you get the runtime reference error when you try to create them.

To work around this you can declare "dummy" vars of the classes you want to compile, or if using the flex compiler there are options to include the classes you are missing.

e.g. declare these anywhere in your project

private var p1:Product1Class;
private var p2:Product2Class;

Its a frustrating problem, if your classes extend MovieClip which is a dynamic class you might be able to access the properties etc by doing something like this:

var product:MovieClip = new productReference() as MovieClip;
p1["someCustomProperty"]; //Dot notation might work here as it is a dynamic class

Answer 3

Chris is absolutely right, the ReferenceError is actually being thrown during the call to getDefinitionByName, meaning that the reflection method cannot find Product1Class or Product2Class in your application domain. You can always check if a definition is available by checking the application domain directly, like:

// inside your createProduct method, yields 'false'.
ApplicationDomain.currentDomain.hasDefinition( productClassName );

Are these library assets loaded in at runtime? If so, you can either make sure that the library swf is loaded into the current application domain by adding an appropriately configured LoaderContext to your Loader, or you can replace the call to getDefinitionByName with the loaded swf's application domain's getDefinition method.