AddHostObjectToScript - how can I pass a typed array to a method of the host object?

[Arakula]

I am currently trying to pass a UInt8Array from JavaScript back to my program. The host object exposes the following method:

[id(21)] ULONG SaveImageAs(VARIANT arrayImage, BSTR fileName);

(not hard to see what it should do ...). The object is added to the WebView2 window using the name "ImgSave" - works nicely.

Okay, over to the JavaScript side ... distilled down, it does the following:

    	const a = new Uint8Array(r.result);
    	const hostObj = window.chrome.webview.hostObjects.ImgSave;
    	const resultValue = await hostObj.SaveImageAs(a, "schmafu.jpg");

... and the host object method is called with ... something. While the file name comes in nicely, the "something" coming in as the arrayImage parameter is a VT_DISPATCH, and I can't find out what exactly is hidden behind that. I'm no COM expert, so I'm sorry if I'm missing the obvious here ... but:

How can I get to the data that should be passed in? Calling pDisp->QueryInterface(IID_IDispatchEx, (void **)&pDispEx); doesn't work, pDisp->GetTypeInfoCount(&tic); doesn't work, using pDisp->GetIDsOfNames(IID_NULL, pszArgs, _countof(pszArgs), LOCALE_USER_DEFAULT, dispIds); doesn't work for anything I can think up (like "value", "name", "length", "buffer", "byteLength").

So ... two questions:

• what would be the best way to pass a UInt8Array (or any typed array, for that matter) to the host object method?
• if my VARIANT method is the best, then how can I access the variables and functions of the JavaScript object that lies behind the incoming LPDISPATCH?

Thank you!

[champnic]

Hey @Arakula - thanks for the question! If you send a non-typed regular javascript array, what do you get in SaveImageAs?

@david-risney Thoughts?

[Arakula]

If I send an array, like so ...

    var testarr = [ 1, 2, 3 ];
    const hostObj = window.chrome.webview.hostObjects.ImgSave;
    const resultValue = await hostObj.SaveImageAs(testarr, "schmafu.png");

I get a (VT_VARIANT | VT_ARRAY) with pArray->cDims=1 and rgsabound[0].cbElements=3. Each element comes in as a VT_I4.

[champnic]

Would you be able to use a regular array like that?

Can you try adding another property onto the UInt8Array object (like arr.MyValue = "hello") and see if you can GetIDsOfNames for MyValue? I'm wondering if we are stripping out the built-in values from JS objects when we expose it as IDispatch.

[Arakula]

We already got another circumvention in place - passing the image data as a base64-encoded string. That works, but is a bit suboptimal.

If I add arr.MyValue = "hello" to the UInt8Array, then yes, I get the ID of MyValue; it's 1, indicating that there's not much else available. To rule out an alphasorted list, I also tried arr.AAA and arr.zzz, which came in with IDs 1 and 2.

So, if you're stripping out the built-in values, and don't offer IDispatchEx or GetTypeInfoCount()/GetTypeInfo(), I'd be very interested in how the host side is supposed to determine what it received and what it can do with it.

[tonyhallett]

For those using C#, type the array as an object[]