HTML Bridge not working with cross-domain Silverlight XAP - silverlight

Question

I've got a complex Silverlight app that uses the HTML bridge functionality quite extensively (in both directions). The app runs fine when the hosting page is from the same domain as the XAP source. Unfortunately, I can't get the HTML bridge functionality to work when the hosting page is on a different domain.
Now, I know the various tricks normally required to get this to work, i.e., everything that's documented here: http://msdn.microsoft.com/en-us/library/cc645023(VS.95).aspx. I've even put together my own simplified cross-domain repro that I was hoping would highlight the problem, but unfortunately, my "repro" works, i.e., both JS->SL and SL->JS functionality work just fine in it, even if the XAP is hosted on a different domain.
Here's what I've tried so far to narrow down the problem:
On my production solution (where I'm having the problem):
Confirmed that "EnableHtmlAccess" is set to true in the <object> tag.
Confirmed that "ExternalCallersFromCrossDomain" is set to "ScriptableOnly" in the AppManifest.xml file.
On my repro solution (where I can't get it to have the problem):
Added multiple libraries with multiple registered scriptable objects.
Added events to the registered objects.
On both:
Tried it with a static <object> tag and with a dynamically created <object> tag (via Silverlight.js).
Tried it with and without specifying handlers for onSourceDownloadProgressChanged, onSourceDownloadComplete, onError, and onLoad.
Tried it with and without a splashscreen.
I'm kinda running out of ideas. Anyone have any suggestions for other troubleshooting steps?

Answer 1

Well, so far I haven't been able to track down the precise difference between the working and the non-working versions. But I came up with a workaround that's sufficient for my needs. As it turns out, only the JS->SL functionality was broken; any calls from SL->JS still worked. So what I did was to register the scriptable SL objects from within Silverlight. In my controlling JavaScript class, I created a function with a unique name, and registered it with the window object:
var mLoadingController;
var mAppId = 'alantaClient_' + Alanta.makeId();
var mSetLoadingControllerId = mAppId + '_SetLoadingController';
window[mSetLoadingControllerId] = function (value) {
mLoadingController = value;
onLoad();
};
And then I pass in the name of the function as a part of the Silverlight app's InitParams:
var initParams = 'setLoadingControllerId=' + mSetLoadingControllerId;
Silverlight.createObject(mSource, mAppHost, mAppId, params, events, initParams);
And then I call that registration function from within Silverlight, like so:
// Do everything necessary to make the LoadingController scriptable.
HtmlPage.RegisterScriptableObject("LoadingController", LoadingController.Instance);
string setLoadingControllerId;
if (e.InitParams.TryGetValue(LoaderConstants.SetLoadingControllerIdReference, out setLoadingControllerId))
{
HtmlPage.Window.Invoke(setLoadingControllerId, LoadingController.Instance);
}
And then I can call it from JS, like so:
mLoadingController.GoToRoom();
Kinda hacky, but it works. Close enough for now.