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IDispatch & default method

emperoremperor Member Posts: 59
Hey there, I'm fairly new to COM/ActiveX etc, and I have a question which is probably quite easy. First off, I'm using Visual C++ and the app I am writing has a WebBrowser control embedded in a dialog box. What I want to do is suppress the right-click menu in the WebBrowser window, and I got as far as finding the "oncontextmenu" property of IHTMLElement2. Thing is, according to MSDN, the put_oncontextmenu() function needs to be passed a "VARIANT of type VT_DISPATCH that specifies the IDispatch interface of an object with a default method that is invoked when the event occurs."

All I want is to give put_oncontextmenu() a function which does nothing, but it wants all this IDispatch stuff which seems awfully complicated (I know it's necessary but it's a pain in C++). I know how to use VARIANT but I don't know anything about IDispatch, or how to pass put_oncontextmenu() an IDispatch which does nothing.

Any help appreciated!


  • oded_sharonoded_sharon Member Posts: 1
    Ok.. I'm a newbie to ATL, but I am currently writing a small project to learn the basics. So in any case I can't vouch for the quality of the code, but here is the simplest example I can think of that would get the job done:

    I use the attribute feature, since it really is a time saver in terms of managing files:

    So first you need an interface with a default method. As far as I could figure out giving the id DISPID_VALUE (0) makes it the default method called

    dual, helpstring("IElementOnPropertyChangeOverride Interface"),
    __interface IElementOnPropertyChangeOverride : IDispatch
    [id(DISPID_VALUE)] HRESULT OnPropertyChange();

    Next you need to implement the interface it is easiet to let ATL implement the IDispatch interface

    vi_progid("???.????"), progid("???.???.1"),
    helpstring("ElementOnPropertyChangeOverride Class")
    class ATL_NO_VTABLE CElementOnPropertyChangeOverride :
    public IElementOnPropertyChangeOverride
    CElementOnPropertyChangeOverride() {}
    HRESULT FinalConstruct() {return S_OK;}
    void FinalRelease() {}

    STDMETHODIMP OnPropertyChange()
    MessageBox(NULL, L"Hello", L"World!", MB_OK);
    return S_OK;


    Finally in your code you need to put this COM object in a Variant and pass it to an HTML Element

    It should probably look something like this

    //access the IHTMLElement2 inteface from a pointer to a DOMElement
    CComPtr spHTMLElement2;
    HRESULT hr = pDOMPtr->QueryInterface(&spHTMLElement2);
    if (FAILED(hr))
    return hr;

    //override function
    CComObject* newMethod(NULL);

    CComVariant newPropertyChange(newMethod);
    hr = spHTMLElement2->put_onpropertychange(newPropertyChange);
    return hr;

    I hope this helps.
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