WTL Class for ActiveX Hosting

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Introduction

WTL is the best library for Win32 Programming I have seen, simple and powerful. But sometimes during a period of time I have to change my mind and work with other libraries and tools, and then I forget some basic ATL/WTL concepts like:

• Event Sink implementations
• ActiveX instancing
• Other basic hard-to-forget concepts

For this reason I'm developing a little library in a WTL like fashion that will help me, (and maybe someone out there), to make my life easier with WTL.

CWTLAxControl

This class and other related classes in this article will help you to make your job with ActiveX controls easier.

CWTLAxControl is a class that implements :

• SmartPointer ( CComPtr<> ).
• CWindowImpl<> ( CAxWindow ).
• IDispEventImpl<>.

Maybe it seems to be a hard class to use , but wait a minute and take a look at the next IExplorer implementation, using this class you will have access to the IWebBrowser2 methods interface via "->" ( smart pointer ), window messages handling (Host window) and Sink Events events fired from ActiveX hosted to your own event handlers.

#define EVENTFN void __stdcall

class CWTLIExplorer : public CWTLAxControl<CWTLIExplorer,IWebBrowser2>
{
    public:
        // BEGIN_MSG_MAP() ... END_MSG_MAP() is optional
        
        BEGIN_MSG_MAP( CWTLIExplorer  )            
            MESSAGE_HANDLER(WM_CREATE,OnCreate) 
        END_MSG_MAP() 
        
        LRESULT OnCreate(UINT uMsg, WPARAM wParam , LPARAM lParam,
                BOOL& bHandled) 
        { 

            // First you must call CWTLAxControl<...,...>::OnCreate 
            // ( it set bHandled = true )

            return CWTLAxControl<CWTLIExplorer,IWebBrowser2,>::OnCreate(
                    uMsg, wParam, lParam, bHandled );
        }

        // SINK_ENTRY(...,...,...) is optional, BEGIN_SINK_MAP()
        // ... should be there

        BEGIN_SINK_MAP( CWTLIExplorer )
            SINK_ENTRY(0, DISPID_NAVIGATECOMPLETE2, OnNavigateComplete2 )
        END_SINK_MAP()
        
        EVENTFN OnNavigateComplete2( IDispatch* pDisp,  VARIANT* URL )
        {
            MessageBox( "OnNavigateComplete2" );
        }
};

Inside CWTLAxControl

Well, if you like the above implementation then it is time to get a more detailed view of how it works.

The first step is to take a look into the main parent class CWTLAxControl that looks like:

template <class T, class Interface>
class CWTLAxControl :    public CComPtr<Interface>,
            public CWindowImpl<CWTLAxControl,CAxWindow>, 
            public CWTLDispEventHelper<T,Interface>
{
    public:

    BEGIN_MSG_MAP(CWTLAxControl)
        MESSAGE_HANDLER(WM_CREATE, OnCreate)
    END_MSG_MAP()

    LRESULT OnCreate( UINT uMsg, WPARAM wParam , LPARAM lParam, 
           BOOL & bHandled )
    {
        LRESULT lRet;
        // We must call DefWindowProc before we can attach to the control.
        lRet = DefWindowProc( uMsg, wParam,lParam );
        // Get the Pointer to the control with Events (true)
        AttachControl(true);
        return lRet;
    }


    HRESULT AttachControl( BOOL bWithEvents = false ) 
    {
        HRESULT hr = S_OK;
        CComPtr<IUnknown> spUnk;
        // Get the IUnknown interface of control
        hr |= AtlAxGetControl( m_hWnd, &spUnk);

        if (SUCCEEDED(hr))
            // Query our interface
            hr |= spUnk->QueryInterface( __uuidof(Interface), 
                   (void**) (CComPtr<Interface>*)this);

        if ( bWithEvents && ! FAILED(hr) )
             // Start events
             hr|= EasyAdvise( spUnk );

        return hr;
    };
};

This class helps us to attach our CComPtr to the ActiveX control using the AttachControl method when it receives the WM_CREATE message. Furthermore this class is derived from CWindowImpl that give us the chance to handle all the windows messages that we'll need.

The last class CWTLDispEventHelper will help us to setup the correct IDispEventImpl implementation.

Inside CWTLDispEventHelper

This class will help us to setup the Event Sink for our control and looks like:

template <class T,class Interface>
class CWTLDispEventHelper : public IDispEventImpl<0,T>
{
    public:
                CComPtr<IUnknown> m_pUnk;
        
        HRESULT EasyAdvise(IUnknown* pUnk) 
        {  
            m_pUnk = pUnk;
            AtlGetObjectSourceInterface(pUnk,&m_libid, &m_iid, 
                 &m_wMajorVerNum, &m_wMinorVerNum);
            return DispEventAdvise(pUnk, &m_iid);
        }
        HRESULT EasyUnadvise() 
        { 
            AtlGetObjectSourceInterface(m_pUnk,&m_libid, 
                  &m_iid, &m_wMajorVerNum, &m_wMinorVerNum);
            return DispEventUnadvise(pUnk, &m_iid);
      }

};

It has only two methods EasyAdvise to setup the Event Sink handler and EasyUnadvise to deactivate it.

How to create the Control

Well, this is the easiest thing, the normal way we use to create any window in WTL:

[...]
CWTLIExplorer  m_pBrowser;
[...].            
m_pBrowser.Create(    m_hWnd, rcDefault, _T("about:blank"),
        WS_HSCROLL| WS_VSCROLL| WS_CHILD | WS_VISIBLE | 
        WS_CLIPSIBLINGS | WS_CLIPCHILDREN );
m_pBrowser->Navigate(_bstr_t("http://www.codeproject.com"),NULL,
        NULL,NULL,NULL);

We can change the _T("about:blank") by the CLSID of the control we want to create "{XXXXX-XXXXX-XXXXX...}".

Closing Words

Well, I expect you will find this article useful and helpful for you, if this is the case and you find anything wrong here, please, send me an email and I will be very happy to solve the mistake and re-upload this article. Bye!