MFC

MFC对IOleObject::SetClientSite()的实现包含对虚函数COleControl::OnSetClientSite()的调用。这时候可以根据m_pClientSite是否为空指针来判断控件是被加载还是被清除。

// CMyControl 派生于COleControl.

void CMyControl::OnSetClientSite()

{

    if (m_pClientSite)

//父窗口及其大小并不重要，因为控件在本地激活时会自动重画和重新定位。

       VERIFY (CreateControlWindow (::GetDesktopWindow(), CRect(,,,), CRect(,,,)));

    else

        DestroyWindow();

    COleControl::OnSetClientSite();

}

ATL

ATL对IOleObject::SetClientSite()的实现有一个IOleClientSite类型的参数(MFC在对IOleObject::SetClientSite()的实现中保存这个指针到COleControl::m_pClientSite)，直接拿来判断就行了。同时，ATL没有重新设置控件的父窗口，所以控件需要手动进行本地激活。

// CMyControl 派生于CComControl

STDMETHOD(SetClientSite)(IOleClientSite *pClientSite)

{

    if (pClientSite)

    {

        RECT rc = {,,,};

        // Don't have access to the Container's window so just use the

        // desktop. Window will be resized correctly during in-place

        // activation.

        HWND hWnd = CreateControlWindow(::GetDesktopWindow(), rc);

        _ASSERT (hWnd);

    }

    else

        ::DestroyWindow(m_hWnd);

     return IOleObjectImpl::SetClientSite (pClientSite);

}

HRESULT InPlaceActivate(LONG iVerb, const RECT* prcPosRect)

{

     // Get the container's window. _ASSERT (m_spClientSite);

     LPOLEINPLACESITE pInPlaceSite = NULL;

     HRESULT hr = m_spClientSite->QueryInterface(IID_IOleInPlaceSite, (void **)&pInPlaceSite);

     _ASSERT (SUCCEEDED (hr) && pInPlaceSite);

     HWND hParent = NULL;

     hr = pInPlaceSite->GetWindow (&hParent);

     _ASSERT (SUCCEEDED (hr) && hParent);

     pInPlaceSite->Release ();

     // Set container window as our parent window

     SetParent (hParent);  < BR >      return CComControlBase::InPlaceActivate(iVerb, prcPosRect);  < BR >

}