Query the Loaded Classes in Flex / AS3

One of the things I love most about programming is running into walls and then finding creative ways to get over (or through) them. The most recent wall I ran into with Flex was that I wanted to be able to find classes at runtime that either implement a given interface or have specific metadata on them. Flash Player doesn’t provide an API to do this directly so I went searching for a workaround. Christophe Herreman tipped me off to a few great utilities for doing this:

A Flex application (using the Flex framework or AS3 only) can use getDefinitionNames to query any loaded SWF file (Application, Module, etc) for its class definitions. The getDefinitionNames utility just parses through the loaded bytecode and finds the class definitions. Then the as3-commons-reflect library can help determine which of those classes implement a given interface or have specific metadata on them. Here is an example:

(source code)

Here is how it works:

    var a:Array = getDefinitionNames(systemManager.loaderInfo);
 
    allClasses.dataProvider = a;
 
    ifooClasses.dataProvider = new ArrayCollection();
    metafooClasses.dataProvider = new ArrayCollection();
 
    for each (var cn:String in a)
    {
      var t:Type = Type.forName(cn);
      for each (var md:MetaData in t.metaData)
      {
        if (md.name == "MetaFoo")
        {
          metafooClasses.dataProvider.addItem(cn);
          break;
        }
      }
 
      if (ClassUtils.getImplementedInterfaceNames(t.clazz).indexOf("IFoo") >= 0)
      {
        ifooClasses.dataProvider.addItem(cn);
      }
    }

Pretty cool! There are a number of fun uses for this kind of thing… Modular IOC containers, client-side plugins, etc.

Getting over this wall was pretty easy thanks to Denis and Christophe. The Flex / AS3 community rocks!