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.

Answer 2

If you just need to be able to read the object fields, the most flexible way is to use JSON.

On your web page side use:

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

On your C++ side define myMethod() to accept a single string argument. Then use a C++ JSON parser to parse this argument into a readable object.

Answer 3

static HRESULT \
IDispatch_VarGet (IDispatch *pRDisp, LPOLESTR Name, VARIANT *pVarRes)
{
    DISPPARAMS DispParams;
    DISPID dispid;
    HRESULT hr;

    if ((hr = IDispatch_GetIDsOfNames (pRDisp, &IID_NULL,
                &Name, 1, LOCALE_SYSTEM_DEFAULT, &dispid)))
        return hr;

    ZeroMemory (&DispParams, sizeof (DispParams));

    hr = IDispatch_Invoke (pRDisp, dispid, &IID_NULL,
            LOCALE_SYSTEM_DEFAULT, DISPATCH_PROPERTYGET,
            &DispParams, pVarRes, NULL, NULL);

    return hr;
}


static HRESULT \
IDispatch_VarPut (IDispatch *pRDisp, LPOLESTR Name, VARIANT *pVarArg)
{
    DISPPARAMS DispParams;
    DISPID dispid, ndispid;
    HRESULT hr;

    if ((hr = IDispatch_GetIDsOfNames (pRDisp, &IID_NULL,
                &Name, 1, LOCALE_SYSTEM_DEFAULT, &dispid)))
        return hr;

    ndispid = DISPID_PROPERTYPUT;

    DispParams.rgvarg = pVarArg;
    DispParams.rgdispidNamedArgs = &ndispid;
    DispParams.cArgs  = 1;
    DispParams.cNamedArgs = 1;

    hr = IDispatch_Invoke (pRDisp, dispid, &IID_NULL,
            LOCALE_SYSTEM_DEFAULT, DISPATCH_PROPERTYPUT,
            &DispParams, NULL, NULL, NULL);

    return hr;
}


static HRESULT \
IDispatch_StrPut (IDispatch *pRDisp, LPOLESTR Name, LPOLESTR StrVal)
{
    VARIANT varg;
    HRESULT hr;

    VariantInit (&varg);

    V_VT   (&varg) = VT_BSTR;
    V_BSTR (&varg) = SysAllocString (StrVal);

    hr = IDispatch_VarPut (pRDisp, Name, &varg);

    VariantClear (&varg);

    return hr;
}


static HRESULT \
IDispatch_IntPut (IDispatch *pRDisp, LPOLESTR Name, int IntVal)
{
    VARIANT varg;
    HRESULT hr;

    VariantInit (&varg);

    V_VT (&varg) = VT_I4;
    V_I4 (&varg) = IntVal;

    hr = IDispatch_VarPut (pRDisp, Name, &varg);

    VariantClear (&varg);

    return hr;
}

...

if ((hr = IDispatch_StrPut (pRDisp, L"code", buff)))
    return hr;

if ((hr = IDispatch_IntPut (pRDisp, L"state", state)))
    return hr;

...

{
    // ...
    VariantInit (&varg);

    if ((hr = IDispatch_VarGet (pRDisp, L"code", &varg)))
    {
        VariantClear (&varg);
        return hr;
    }

    if (V_VT (&varg) == VT_BSTR)

    // ...

    VariantClear (&varg);
    return hr;
}

and jave code sample...

var frec = {code:'', state:0};

frec.code = row.cells[0].innerHTML;
external.FeatureStateChg (frec);
_featState (row.cells[2], frec.state);

...

var frec = {code:'', name:'', state:0};

if (!external.FeaturesEnum (frec, i))
    break;