Question

Basically I want to develop a BHO that validates certain fields on a form and auto-places disposable e-mails in the appropriate fields (more for my own knowledge). So in the DOCUMENTCOMPLETE event I have this:

for(long i = 0; i < *len; i++)
{
    VARIANT* name = new VARIANT();
    name->vt = VT_I4;
    name->intVal = i;
    VARIANT* id = new VARIANT();
    id->vt = VT_I4;
    id->intVal = 0;
    IDispatch* disp = 0;
    IHTMLFormElement* form = 0;
    HRESULT r = forms->item(*name,*id,&disp);
    if(S_OK != r)
    {
        MessageBox(0,L"Failed to get form dispatch",L"",0);// debug only
        continue;
    }
    disp->QueryInterface(IID_IHTMLFormElement2,(void**)&form);
    if(form == 0)
    {
        MessageBox(0,L"Failed to get form element from dispatch",L"",0);// debug only
        continue;
    }

    // Code to listen for onsubmit events here...         
}

How would I use the IHTMLFormElement interface to listen for the onsubmit event?

Answer 1

Once you have the pointer to the element you want to sink events for, you would QueryInterface() it for IConnectionPointContainer and then connect to that:

REFIID riid = DIID_HTMLFormElementEvents2;
CComPtr<IConnectionPointContainer> spcpc;
HRESULT hr = form->QueryInterface(IID_IConnectionPointContainer, (void**)&spcpc);
if (SUCCEEDED(hr))
{
    CComPtr<IConnectionPoint> spcp;
    hr = spcpc->FindConnectionPoint(riid, &spcp);
    if (SUCCEEDED(hr))
    {
        DWORD dwCookie;
        hr = pcp->Advise((IDispatch *)this, &dwCookie);
    }
}

Some notes:

1. You probably want to cache dwCookie and cpc, since you need them later when you call pcp->Unadvise() to disconnect the sink.
2. In the call to pcp->Advise() above, I pass this. You can use any object you have that implements IDispatch, which may or may not be this object. Design left to you.
3. riid will be the event dispinterface you want to sink. In this case, you probably want DIID_HTMLFormElementEvents2.

Here’s how to disconnect:

pcp->Unadvise(dwCookie);

Let me know if you have further questions.

Edit-1:

Yeah, that DIID was wrong. It should be: DIID_HTMLFormElementEvents2.

Here is how I found it:

C:\Program Files (x86)\Microsoft Visual Studio 8\VC\PlatformSDK>findstr /spin /c:"Events2" *.h | findstr /i /c:"form"