Passing an object from Javascript to C++

Question

I have found Passing an array from Javascript to C++ solution, but I have another task: Passing an object from Javascript to C++ (if I use IWebBrowser2 with IDispatch)

I mean that I need call C++ method via window.external.method with JavaScript object argument

var obj = {name: "Petr", group: "Friend"};
window.external.myMethod(obj);

How to get access to object member "name", "group", etc. ?

Answer 1

You can access the object's properties via the IDispatch interface and its methods GetIDsOfNames and Invoke.

Depending on your definition of myMethod, you should be receiving obj as either a VARIANT or an IDispatch * in your C++ code. If a VARIANT, vt should be VT_DISPACTH, in which case you can safely dereference pdispval.

Once you have an IDispatch pointer, you can use GetIDsOfNames to get the DISPID for a property that you're interested in like so:

_bstr_t sPropertyName = L"myProperty";
DISPID dispid = 0;
HRESULT hr = pDispatch->GetIDsOfNames(IID_NULL, &sPropertyName, 1, LOCALE_SYSTEM_DEFAULT, &dispid);
if(SUCCEEDED(hr))
{
    ...

Once you have successfully received your DISPID, you must call Invoke differently according to whether you would like to get a value, set a value or call a method.

For instance, to get a value:

    VARIANT vValue;
    hr = pDispatch->Invoke(dispid, IID_NULL, LOCALE_SYSTEM_DEFAULT, DISPATCH_PROPERTYGET, 0, &vValue, 0, 0);
    if(SUCCEEDED(hr))
    {
        ...

See the documentation for Invoke for more information about the different permutations when calling it.