How can I tell if an instance implements an interface in ActionScript 3.0

Question

I am overriding the addItem() function of an array collection and I would like to detect if the added item implements a particular interface.

Previously I used the, is operator to detect the class type, but now that I am using an interface for classes I would rather test to see if the object implements the interface.

I expect I could just try and cast the object as the interface and see if it's not null. Is this the best way to do it?

I could also just create a new addFunction() that only accepts objects of the interface type.

Answer 1

You can still use is to test for an interface.

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark" xmlns:mx="library://ns.adobe.com/flex/halo" minWidth="1024" minHeight="768" creationComplete="application1_creationCompleteHandler(event)">
    <fx:Script>
     <![CDATA[
      import mx.events.FlexEvent;
      public var test:TestInterface = new TestInterface() //implements ITestInterface


      protected function application1_creationCompleteHandler(event:FlexEvent):void
      {
       trace(test is ITestInterface); //true
      }

     ]]>
    </fx:Script>
</s:Application>

Answer 2

To add to the answer of Joel: if you want more information about the interfaces a class implements (and its subclasses, parent classes, etc), the AS3Commons library has a ClassUtils class that has a number of convenience methods.