ExternalInterface for Scorm 1.2 LMS Communication

Hi OrangeHaze,

ExternalInterface usage really hangs on one thing: serialization. The
EI system does automatic data serialization in/out of Flash. That is,
when you create an Object instance in Flash, JavaScript gets it as an
object. When you create a Number, a number is received in JavaScript.
This is where the majority of the processing overhead comes from. Yes,
ExternalInterface makes it a bit easier to invoke functions
bi-directionally, and it does have the neat feature of returning values
directly from function invocation rather than asynchronously, but other
than that there's not much else to it.

So, if you are only ever passing strings between Flash and JavaScript
and only call a handfull of functions, fscommand and getURL are better
because that entire step of cross-converting values (using XML as
intermediary) is avoided. However, if you need flexibility,
ExternalInterface is just the thing. It is not the ONLY thing, though.
I've made extensive use of JSON in past code and I think that it could
be argued that it has advantages. It also does serialization but it does
it to a native serialized format of JavaScript. This means that the
processing overhead for JSON is considerably less than for
ExternalInterface. For sheer speed, JSON is great, but for flexibility,
it could still use some work. Adding a callback, for example, is not
something that's built into JSON because it's so generic. Also, direct
function call return values are not supported like they are in
ExternalInterface. So the decision is basically one that involves three
factors:

1. If you want sheer speed, only call a few functions, and parameters
are only ever strings: use getURL or fscommand
2. If you want greatest flexibility and integration, most native
language support, and ease of use: use ExternalInterface
3. If you want a mixture between speed and integration but with less of
each than #1 and #2: use JSON

Hope that was helpful.

Regards,
Patrick

--
http://www.baynewmedia.com
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OrangeHaze wrote:
> Hello, I've been doing a large amount of research concerning Flash <-> LMS
> communication via ExternalInterface. Originally ExternalInterface was not even
> an option for my company, since our client requested the SCO be published in
> Flash 7, but we have recently convinced them to upgrade to Flash 8 (and I'm
> actually still pushing for Flash 9).
>
>
> The decision I am facing is whether or not I should implement the
> ExternalInterface class, or should I just stick with the old FSCommand. I
> understand that the ExternalInterface is a no-brainer if you need to support
> browsers other than IE; however, that is not the case for us because our LMS
> provider only supports IE.
>
> Personally I would like to start using ExternalInterface because Adobe seems
> to advocate it as the best way to communicate with Javascript, but I've read an
> article that says ExternalInterface is much slower than FSCommands or GetURLs
> (in milliseconds at least), and I also wanted to investigate and find out if
> anyone has implemented ExternalInterface when working with a Javascript Runtime
> Wrapper.
>
> I also understand that ExternalInterface is synchronous, so does that mean my
> SWF is guaranteed to receive the LMS's variables back, or at least more
> consistently than FSCommands?
>
> If anyone has some experience on this subject, I would greatly appreciate your
> input. Until then I am thinking about just replacing the FSCommands with a
> ExternalInterface.call() method, and passing my variables to the Javascript
> Function responsible for hooking the FSCommands (I believe it is
> MovieName_DoFSCommand()), and letting Javascript take care of setting the
> variables I pass it. Although if I do this, I fear I might missing out on the
> benefits of the synchronizing unless I rewrite the Javascript function so it
> returns a value immediately instead of using SetVariable() on the movie object.
> Please let me know what you think!!
>
>
> ExternalInterface.call("Main_DoFSCommand", "LMSGetValue",
> "cmi.suspend_data,_root.vModStatus");
>