How to extend the functionality of the Windows shell by using a context menu handler in Visual C++ (298109)

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The following files are available for download from the Microsoft Download Center:

Visual C++ 6.0

Download the Rscontext.exe package now.
For more information about how to download Microsoft support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file. The RSContext sample is an ATL DLL project created with Visual C++ 6.0 with Service Pack 5. The "RS" is short for RegisterServer. The project can be rebuilt and registered from the sample files and will be loaded by Windows Explorer when a context menu is displayed for .dll and .ocx files.

The new context menu items will be called Register and Unregister. The implementation will look for Regsvr32.exe and try to register and unregister these file types with COM. Normally, Regsvr32.exe is located in the System32 folder for Windows NT, Windows 2000, and Windows XP-based systems or the System folder for Windows 95, Windows 98 or Windows Millennium Edition-based computers, so it should not be necessary to include the full path to the module, but it can be added if necessary.

The following steps demonstrate creation of a simple context menu handler.

1. Create an ATL DLL project and add a simple object with all the defaults. Include shlobj.h and comdef.h in stdafx.h. Then add two more interfaces to inherit from: IShellExtInit and IContextMenu:

   public IShellExtInit,
   public IContextMenu,
   						

   Add these interfaces to the COM map as well:

   COM_INTERFACE_ENTRY(IShellExtInit)
   COM_INTERFACE_ENTRY(IContextMenu)
   					

2. The IShellExtInit interface has one method, called Initialize(). Initialize receives three parameters: an ITEMIDLIST, an IDataObject, and a ProgID registry key (if one exists). The Initialize method must just store the file name so DragQueryFile can be called on the IDataObject pointer to retrieve it.
   
   IContextMenu has three methods: GetCommandString, InvokeCommand, and QueryContextMenu. QueryContextMenu inserts the new menu options, GetCommandString asks for help text for the options, and InvokeCommand executes the option the user selected.
   
   Declare the methods in the class header:

   // IContextMenu
   STDMETHOD(GetCommandString)(UINT idCmd, UINT uFlags, 
                UINT *pwReserved, LPSTR pszName, UINT cchMax);
   STDMETHOD(InvokeCommand)(LPCMINVOKECOMMANDINFO pici);
   STDMETHOD(QueryContextMenu)(HMENU hmenu, UINT indexMenu, 
   			UINT idCmdFirst, UINT idCmdLast, 
   					UINT uFlags);
   
   // IShellExtInit
   STDMETHOD(Initialize)(LPCITEMIDLIST pidlFolder, 
                            LPDATAOBJECT lpdobj, 
   		      HKEY hkeyProgID);
   					

3. In addition, add a member variable to hold the file name:

   TCHAR m_szFile[MAX_PATH];
   					

   NoteDragQueryFile retrieves the full path name of the file.
4. Implement the methods as follows:

   HRESULT CRSMenu::QueryContextMenu(HMENU hmenu, UINT indexMenu,
   					       UINT idCmdFirst,
                                                  UINT idCmdLast,
   					       UINT uFlags)
   {
   	if (!(CMF_DEFAULTONLY & uFlags))
   	{
   		int nCmdRegister = idCmdFirst;
   		int nCmdUnregister = idCmdFirst+1;
   
   		InsertMenu(hmenu, indexMenu++, MF_STRING|MF_BYPOSITION,
   				nCmdRegister, _T("&Register"));
   		InsertMenu(hmenu, indexMenu++, MF_STRING|MF_BYPOSITION,
   				nCmdUnregister, _T("&Unregister"));
   
                   // A successful return code should be the offset of
                   // the largest command identifier assigned, plus one
   		return MAKE_HRESULT(SEVERITY_SUCCESS, FACILITY_NULL,
                                      nCmdUnregister - idCmdFirst + 1);
   	}
   	
   	return MAKE_HRESULT(SEVERITY_SUCCESS,
                               FACILITY_NULL, USHORT(0));
   }
   
   HRESULT CRSMenu::InvokeCommand(LPCMINVOKECOMMANDINFO pici)
   {
   	TCHAR szParms[MAX_PATH+6];
   
           // The offset will determine which option was requested:
           // 0 for Register, 1 for Unregister
   	UINT idOffset = LOWORD(pici->lpVerb);
   
           // Embed a '/u' for the Unregister command into the
           // parameters, and always put quotes around the path
           // so spaces in the path won't be a problem
   	if (1 == idOffset)
   	{
   		lstrcpy(szParms, _T("/u \""));
   		lstrcat(szParms, m_szFile);
                   lstrcat(szParms, _T("\""));
   	}
   	else
           {
                   lstrcpy(szParms, _T("\""));
   		lstrcat(szParms, m_szFile);
                   lstrcat(szParms, _T("\""));
           }
   	ShellExecute(pici->hwnd, NULL, _T("regsvr32.exe"), szParms,
   					NULL, 0);
   
   	return S_OK;
   }
   
   HRESULT CRSMenu::GetCommandString(UINT idCmd, UINT uFlags, 
                                     UINT* pwReserved,
   				  LPSTR pszName, UINT cchMax)
   {
   	if (uFlags & GCS_HELPTEXT)
   	{
                   // Windows NT will ask for Unicode strings
   		switch(idCmd)
   		{
   		case 0:
   			if (uFlags & GCS_VERBA)
   			lstrcpynA(pszName, 
                               "Perform COM registration for this module",
                                    cchMax);
   			else
   			lstrcpynW((LPWSTR)pszName,
                              L"Perform COM registration for this module",
                                    cchMax);
   			break;
   		case 1:
   			if (uFlags & GCS_VERBA)
   			lstrcpynA(pszName,
                              "Perform COM unregistration for this module",
                                   cchMax);
   			else
   			lstrcpynW((LPWSTR)pszName,
                             L"Perform COM unregistration for this module",
                                   cchMax);
   			break;
   		default:
   			break;
   		}
   	}
   
   	return S_OK;
   }
   
   HRESULT CRSMenu::Initialize(LPCITEMIDLIST pidlFolder,
                               LPDATAOBJECT lpdobj, HKEY hkeyProgID)
   {
   	if (lpdobj == NULL)
   		return E_INVALIDARG;
   
           // The file can be referenced through the STGMEDIUM structure
           // that is retrievable through the IDataObject pointer, and
           // DragQueryFile can then be used to retrieve the file name.
   	STGMEDIUM medium;
           FORMATETC fe = {CF_HDROP, NULL, DVASPECT_CONTENT, -1,
                           TYMED_HGLOBAL};
   	HRESULT hr = lpdobj->GetData(&fe, &medium);
   	if (FAILED(hr))
   		return E_INVALIDARG;
   
   	DragQueryFile(reinterpret_cast<HDROP>(medium.hGlobal), 0,
   					m_szFile, MAX_PATH);
   
   	ReleaseStgMedium(&medium);
   	return hr;
   }
   					

5. Add the following to the .rgs file to register the context menu handlers for the file types:

   NoRemove Ocxfile
   {
   	NoRemove Shellex
   	{
   		NoRemove ContextMenuHandlers
   		{
   			{A9F3EE64-2047-49CF-8522-FE41C75C158B}
   		}
   	}
   }
   NoRemove Dllfile
   {
   	NoRemove Shellex
   	{
   		NoRemove ContextMenuHandlers
   		{
   			{A9F3EE64-2047-49CF-8522-FE41C75C158B}
   		}
   	}
   }
   					

6. Build and register the extension and test it with Windows Explorer. The InvokeCommand method runs Regsvr32.exe, which should be in System32 on Windows NT, Windows 2000, or Windows XP, or System on Windows 95, Windows 98, or Windows Millennium Edition, so the full path should not be necessary. The extensions will try to register (or unregister) any .dll or .ocx file. If a .dll does not export DllRegisterServer, the registration will fail, and an error message will appear indicating that either the function is not exported or the file is corrupt. Note that for a non-COM .dll, this failure is normal, and no corrective measures are needed.