这个问题关系到 shell接口编程部分，一个比较令人纠结的问题时，不管操作那个部分的文件夹，都要从shell文件系统的root节点(Desktop)开始操作，直到找到你要的节点位置。概因树形结构表达有关。
不说了，直接上代码吧:
LPITEMIDLIST pidlItems = NULL, pidlURL = NULL,
pidlWorkDir = NULL;
pidlWorkDir = NULL;
ULONG ulParseLen = 0;
HRESULT hr;
TCHAR pszPath[MAX_PATH*2];
DWORD dwPriority = 0, dwFlags = IEIFLAG_SCREEN;
SIZE size = { dwWidth, dwHeight };
IExtractImage* peiURL = NULL; //
interface is used to request a thumbnail image from a Shell folder
interface is used to request a thumbnail image from a Shell folder
IShellFolder* psfDesktop = NULL;
IShellFolder* psfWorkDir = NULL;
IMalloc* pMalloc = NULL;
TString TempTumbnail = GetMediaLibraryDefaultDir() + _T( "MLThumbnail.jpg" );
CImage myImage;
TString wsDir,wsFile,wsTempFile;
BOOL bComInit = TRUE;
hr = CoInitialize( NULL );
hr = SHGetMalloc( &pMalloc );
hr = SHGetDesktopFolder(&psfDesktop);
wsDir = LocalFile;
wsDir.erase(wsDir.find_last_of(_T( '\\' ))
+ 1, wsDir.length());
+ 1, wsDir.length());
wsFile = LocalFile;
wsFile.erase(0, wsFile.find_last_of(_T( '\\' ))
+ 1);
+ 1);
// get working directory
TCHAR m_wsBuffer[255];
_tcscpy_s(m_wsBuffer,wsDir.c_str());
// ParseDisplayName:Translates
a file object's or folder's display name into an item identifier list.
a file object's or folder's display name into an item identifier list.
hr = psfDesktop->ParseDisplayName(NULL, NULL, m_wsBuffer, &ulParseLen, &pidlWorkDir, NULL);
hr = psfDesktop->BindToObject(pidlWorkDir, NULL, IID_IShellFolder, (LPVOID*)&psfWorkDir);
psfDesktop->Release();
psfDesktop = NULL;
pMalloc->Free(pidlWorkDir);
pidlWorkDir = NULL;
// retrieve link information
_tcscpy_s(m_wsBuffer,wsFile.c_str());
hr = psfWorkDir->ParseDisplayName(NULL, NULL, m_wsBuffer, &ulParseLen, &pidlURL, NULL);
// query IExtractImage
hr = psfWorkDir->GetUIObjectOf(NULL, 1, (LPCITEMIDLIST*)&pidlURL, IID_IExtractImage, NULL, (LPVOID*)&peiURL);
// define thumbnail
properties
properties
hr = peiURL->GetLocation(pszPath, MAX_PATH*2, &dwPriority, &size, 16, &dwFlags);
// generate thumbnail
HBITMAP hThumbnail= NULL;
hr = peiURL->Extract(&hThumbnail);
// clean-up IExtractImage
peiURL->Release();
peiURL = NULL;
myImage.Attach(hThumbnail);
myImage.Save(TempTumbnail.c_str());
// free allocated structures
if (peiURL
!= NULL) peiURL->Release();
!= NULL) peiURL->Release();
if (pidlURL
!= NULL) pMalloc->Free(pidlURL);
!= NULL) pMalloc->Free(pidlURL);
if (pidlWorkDir
!= NULL) pMalloc->Free(pidlWorkDir);
!= NULL) pMalloc->Free(pidlWorkDir);
if (psfDesktop
!= NULL) psfDesktop->Release();
!= NULL) psfDesktop->Release();
if (psfWorkDir
!= NULL) psfWorkDir->Release();
!= NULL) psfWorkDir->Release();