R – Preventing error from being thrown in child swf

There is no way to be notified on uncaught exceptions in Flex 3. Adobe are aware of the problem but I don't know if they plan on creating a workaround.

The only solution as it stands is to put try/catch in logical places and make sure you are listening to the ERROR (or FAULT for webservices) event for anything that dispatches them.

Edit: Furthermore, it's actually impossible to catch an error thrown from an event handler. I have logged a bug on the Adobe Bug System.

Update 2010-01-12: Global error handling is now supported in Flash 10.1 and AIR 2.0 (both in beta), and is achieved by subscribing the UNCAUGHT_ERROR event of LoaderInfo.uncaughtErrorEvents. The following code is taken from the code sample on livedocs:

public class UncaughtErrorEventExample extends Sprite
{
    public function UncaughtErrorEventExample()
    {
        loaderInfo.uncaughtErrorEvents.addEventListener(
            UncaughtErrorEvent.UNCAUGHT_ERROR, uncaughtErrorHandler);
    }

    private function uncaughtErrorHandler(event:UncaughtErrorEvent):void
    {
        if (event.error is Error)
        {
            var error:Error = event.error as Error;
            // do something with the error
        }
        else if (event.error is ErrorEvent)
        {
            var errorEvent:ErrorEvent = event.error as ErrorEvent;
            // do something with the error
        }
        else
        {
            // a non-Error, non-ErrorEvent type was thrown and uncaught
        }
    }

The plain answer is "no, you can't". This is because you cannot hide or replace the built-in functions of the player. In theory, you could prevent many such calls by examining DoABC blocks of the SWF and finding calls to URLLoader or navigateToURL and similar. Of course it's impossible to find each one of them as those may be called through reflection. Besides, you'd have to write a decompiler to do that.

1. ActionScript has a very short history of versions, it was only 1.0, 2.0 and 3.0. Flash Player doesn't execute ActionScript. It executes bytecode (ABC - A ctionScript b yte c ode). Apart from ongoing maintainance, there were few changes to ABC format. Most significant are reflected in ABC format specs. So, for example, in Flash Player 10 a group of opcodes aka "Alchemy opcodes" was added, they, however, are not available to the programmers writing in AS3. I'm using this http://www.anotherbigidea.com/javaswf/avm2/AVM2Instructions.html for a quick reference, but it is a bit dated.

2. SWFLoader is a class you want to use when dealing with Flex framework. It is essentially the Loader class, extended to deal with the issues the framework introduced on top of built-ins.