It probably doesn't have to do with Google app engine per se, since the whole thing's running in the browser -- unless there's some sort of server dependency somewhere you haven't mentioned. Assuming that's not the case...
If you're able to get Flash to call into JavaScript with ExternalInterface.call(), but not JavaScript to call back into Flash, then it's probably one or two things: your EI callback & handler aren't wired up properly (in Flash), or your JavaScript doesn't have a handle on the SWF object in the browser.
You might try posting some code, but in the meantime, here's something I know works in both IE and FireFox. First, the browser code:
<html>
<head>
<script language="JavaScript" type="text/javascript">
var swfReady = false;
function callbacksInitialized()
{
swfReady = true;
}
function helloFlash()
{
if (swfReady)
{
// Get a handle on the Flash object
var swfObject = navigator.appName.indexOf("Microsoft") != -1 ? window["HelloMac"] : document["HelloMac"] ;
// Call back into the Flash file
swfObject.helloFlash(document.getElementById("txtMessage").value);
}
}
function helloMac(message)
{
alert(message);
}
</script>
</head>
<body scroll="no">
<div align="center">
<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000"
id="HelloMac" width="600" height="300"
codebase="http://fpdownload.macromedia.com/get/flashplayer/current/swflash.cab">
<param name="movie" value="HelloMac.swf" />
<param name="quality" value="high" />
<param name="bgcolor" value="#869ca7" />
<param name="allowScriptAccess" value="sameDomain" />
<embed src="HelloMac.swf" quality="high" bgcolor="#869ca7"
width="600" height="300" name="HelloMac" align="middle"
play="true"
loop="false"
quality="high"
allowScriptAccess="sameDomain"
type="application/x-shockwave-flash"
pluginspage="http://www.adobe.com/go/getflashplayer">
</embed>
</object>
<br /><br />
<input type="text" id="txtMessage" value="Hello, Flash!" /><br />
<input id="btnSend" type="button" value="Send to Flash" onclick="helloFlash();" />
</div>
</body>
</html>
And now, the Flash code (in my case, it's Flex, so hopefully it's clear):
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" initialize="init()" height="300" width="600">
<mx:Script>
<![CDATA[
import mx.controls.Alert;
import flash.external.ExternalInterface;
private function init():void
{
addCallbacks();
}
private function addCallbacks():void
{
ExternalInterface.addCallback("helloFlash", this_helloFlash);
ExternalInterface.call("callbacksInitialized");
}
// Display a message from the host
private function this_helloFlash(message:String):void
{
Alert.show(message);
}
// Send a string to the host
private function helloMac():void
{
if (ExternalInterface.available)
{
ExternalInterface.call("helloMac", txtMessage.text);
}
}
]]>
</mx:Script>
<mx:VBox horizontalCenter="0" verticalCenter="0">
<mx:TextInput id="txtMessage" text="Hello, Mac!" />
<mx:Button id="btnSend" label="Send to Host" click="helloMac()" />
</mx:VBox>
</mx:Application>
The example demonstrates Flash calling into JavaScript with some text, and JavaScript calling back into Flash in the same way. Some points to pay attention to:
- Make sure you wait to call into
Flash until Flash has notified the
browser it's ready to begin receiving
calls (as indicated by my
callbacksInitialized() method).
- Test to be sure you're using the
appropriate browser-specific object
reference (e.g., window["HelloMac"]
vs. document["HelloMac"]).
Without knowing more, I'm guessing it's one of these two items, since that's been my experience. Hope it helps! I'll keep an eye on the post for follow-ups in case you have any.