Using the Shell Namespace To Get Network Computers, Printers and Recycle Bin Items

Sample Image

Environment: VC6

This article explains how to make use of the COM interfaces
implemented by Shell Extensions to get the required information
on a local machine or network. In this example I have
demonstrated it to get the list of all user machines logged onto
the network, printers attached to network and items in the
recycle bin of local machine. The CShellExt wrapper class can be
extended to include the functionality to extract all kind of
information. Although there are a lot of wrapper shell functions
present to get the same information, but use of COM interfaces
gives an insight into what foes on behind the scene in windows
explorer and how we can extend the shell’s namespace.

Before we ask for any information from Shell, there are couple
of environment variables, which needs to be initialized. First we
need to allocate memory in Shell’s address space. Asking for
IMalloc interface pointer, which we will release before we exit
our application, can do this. The Desktop folder is the root of
Shell’s name space, therefore we will need the interface pointer
to that. These steps have been implemented in
InitializeEnvironment function of CShellExt class.


HRESULT  hr = SHGetMalloc (&m_pMalloc);
HRESULT  hr = SHGetDesktopFolder (&m_pDesktopFolder);

Network Neighborhood, Printers, RecycleBin, etc. fall under
the category of Special Folders a.k.a Virtual Folders. Windows
API provides bunch of functions to work with them. We use
SHGetSpecialFolderPath function to obtain the path to required
folder. E.g. to obtain path to printers folder


HRESULT  hr = SHGetSpecialFolderLocation (NULL, CSIDL_PRINTERS, &netItemIdLst);

To get more information about second argument to this function
call, look in the on-line help. This argument specifies the
special folder for which IShellFolder interface is needed. The
link between special folders and their paths is stored in the
registry as:

HKEY_CURRENT_USER
 \Software
  \Microsoft
   \Windows
     \CurrentVersion
       \Explorer
        \Shell Folders

After we have IShellFolder interface pointer to special
folder, we can ask for contents of folder by creating an item
enumeration object (a set of item identifiers) that can be
retrieved using the IEnumIDList interface. E.g. for printer
folder

HRESULT hr = pPrinterFolder->EnumObjects (NULL, SHCONTF_FOLDERS | SHCONTF_NONFOLDERS, &pEnumIds);

After we have ID list enumeration, the display name for each
item can be obtained by using GetDisplayNameOf method of
IShellFolder interface.

while ((hr = pEnumIds->Next (1, &pidlItems, &celtFetched)) != S_FALSE && celtFetched == 1)
{
   hr = pPrinterFolder->GetDisplayNameOf (pidlItems, SHGDN_INFOLDER, &strDispName);
   if (FAILED (hr))
   {
      goto FreeInterfaces;
   }
   .
   .
}

After we have obtained the display name of the folder, we need
to extract icons. Every shell object which has icon(s) associated
with it, implements IExtractIcon interface. This can be obtained
by using GetUIObjectOf method of IShellFolder interface. After
getting the IExtractIcon interface pointer, use its two methods
to get handles to small and large icons. This has been
implemented in GetIconsForFolderNode function of CShellExt class.

IExtractIcon *pExtractIcon = NULL;

hr = pFolderNode->GetUIObjectOf (NULL, 1, const_cast<LPCITEMIDLIST *>(&pidlItems),
IID_IExtractIcon, NULL, reinterpret_cast<LPVOID *>(&pExtractIcon));

if (SUCCEEDED (hr)) {
	TCHAR str[MAX_PATH] = {0};
	int index;
	UINT flags;

	// Get the file location where the icons are stored.

	hr = pExtractIcon->GetIconLocation (0, str, MAX_PATH, &index, &flags);
	if (SUCCEEDED (hr)) {
		HICON hiconLarge = NULL;
		HICON hiconSmall = NULL;
		UINT nIconSize = MAKELONG (32, 16);
		LPCSTR pszFile = (LPCSTR)str;

		// Extract the icon handles from the location.

		hr = pExtractIcon->Extract (str, index, &hIconLg, &hIconSm, nIconSize);
		pExtractIcon->Release ();
	}
}

To show the use of this extension class, I have created a
dialog-based application, which has a tool bar with 3 buttons for
NetWork compuetrs, Printers, RecycleBin items. Click on one of
them to see the results. The sample application also shows the
usage of CTreeCtrl and how to implement CToolBar in dialog based
applications.

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Download demo project – 28.3 Kb

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