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BUG: Error Accessing Window.external in ATL DHTML Control

Posted 2008/09/18 15:00 by Dave Aitch

SYMPTOMS

A DHTML control created with the ATL Object Wizard fails with the following script error when accessing window.external from Internet Explorer 5.0:
'Object doesn't support this property or method'

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CAUSE

A DHTML control contains two IDispatch interfaces, a default interface for scripting and another for the window.external methods. The WebBrowser control incorrectly uses the default IDispatch interface when invoking window.external methods.

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RESOLUTION

Implement the window.external IDispatch method in a separate COM object.

Use the following steps to implement a sub-object for a default ATL DHTML control project:
1. Add HTML Control to project (Ctrl).
2. Add Simple Object to project, use default of "dual interface" (UIObj).
3. Remove original UI dispatch interface (ICtrlUI) from ctrl.h: From class derivation list: 
   public IDispatchImpl<ICtrlUI, &IID_ICtrlUI, &LIBID_DHTMLCONTROLLib>,
From COM_MAP, replace the following two lines: 
    COM_INTERFACE_ENTRY(ICtrlUI)
    COM_INTERFACE_ENTRY2(IDispatch, ICtrl)

    with
)

       COM_INTERFACE_ENTRY(IDispatch)
4. Move the example OnClick method from ctrl.h to uiobj.h: 
   // ICtrlUI
   public:
// Example method called by the HTML to change the <BODY> background color
   STDMETHOD(OnClick)(IDispatch* pdispBody, VARIANT varColor)
   {
	CComQIPtr<IHTMLBodyElement> spBody(pdispBody);
	if (spBody != NULL)
		spBody->put_bgColor(varColor);
	return S_OK;
   }
5. Modify dhtmlcontrol.idl to reflect above changes: Move OnClick method from ICtrlUI to IUIObj interface definition: 
   // Example method that will be called by the HTML
   HRESULT OnClick([in]IDispatch* pdispBody, [in]VARIANT varColor);
Remove original ICtrlUI interface from interface definition: 
   [
	object, dual,
	uuid(C3920EDB-BAD6-11D2-AFA1-00A0C9C9E6C5),
	helpstring("ICtrlUI Interface"),
	pointer_default(unique)
   ]
   interface ICtrlUI : IDispatch
   {
   };
Remove original ICtrlUI interface from Ctrl coclass: 
   interface ICtrlUI;
6. Modify OnCreate method in Ctrl.h: 
   #include "uiobj.h"
   ...
	LRESULT OnCreate(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM    /*lParam*/, BOOL& /*bHandled*/)
   {
   CAxWindow	wnd(m_hWnd);

   HRESULT hr = wnd.CreateControl(IDH_CTRL);
   if (SUCCEEDED(hr))
   {
   // Create sub-object - this implements our window.external methods to be    called from HTML
   hr = CComObject<CUIObj>::CreateInstance( &m_pUI );
   if ( SUCCEEDED(hr) )
   {
   CComQIPtr<IDispatch>	pDisp(m_pUI);
   hr = wnd.SetExternalDispatch(pDisp);
   }
   }
   if (SUCCEEDED(hr))
   hr = wnd.QueryControl(IID_IWebBrowser2, (void**)&m_spBrowser);
   return SUCCEEDED(hr) ? 0 : -1;
   }
   CComObject<CUIObj>*	m_pUI;
7. In addition, you can specify that this simple object should not be creatable with CoCreateInstance by marking the object as non-creatable.
• Add the [noncreatable] attribute in the IDL file for the simple object's coclass. Don't forget the comma after the help string attribute 
 [
    uuid(....),
    help string("UIObj class"),
    noncreatable
  ]
  coclass UIObj
  {
    ...
  }
• Change OBJECT_ENTRY(CLSID_UIObj, CUIObj)macro in the object map to OBJECT_ENTRY_NON_CREATEABLE(CUIObj) for the simple object.



출처 : http://support.microsoft.com/kb/202009

Filed under : Programming/Win32 API
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