getDefinitionByName() Fails in SWFs Loaded Into Another SWF (Solution)

Just a quick note for future reference. When you are using getDefinitionByName(“ClassName”) inside a SWF that is being loaded into another SWF, it might not find the symbol from its own library (see ApplicationDomain and LoaderContext for why).

The solution is to get a reference from the ApplicationDomain of the SWF being loaded using the getDefinition() method. So the code:

var mySymbol:Class = getDefinitionByName("MySymbol");

becomes…

var mySymbol:Class = loaderInfo.applicationDomain.getDefinition("MySymbol");

Hopefully that resolves any issue you had with getDefinitionByName(). Of course you’d use a similar mechanism to work the other way around, and get at classes inside a loaded SWF. In this case it would be loader.contentLoaderInfo.applicationDomain.getClass()… however this depends on what ApplicationDomain you’ve loaded your child SWF into (see LoaderContext class).

In my case I wanted to attach a different “scroll thumb” symbol for each section SWF in the site I’m working on, so I couldn’t just use a single runtime shared asset.