知识库

IExtractImage

void* CShellListCtrl::GetThumbnailImage(CString &fileName, int longestEdge, int colorDepth)
{
 // divide the file name into a folder path and file name.
 WCHAR wDirName[MAX_PATH];
 WCHAR wFileName[MAX_PATH];
 CString dir = fileName.Left(fileName.ReverseFind(’\\’));
 CString file = fileName.Right(fileName.GetLength() - dir.GetLength() - 1);
 TCHAR tName[MAX_PATH];
 strcpy(tName, dir.GetBuffer());
 wcscpy(wDirName, CT2W(tName));
 
 strcpy(tName, file.GetBuffer());
 wcscpy(wFileName, CT2W(tName));
 IShellFolder* pDesktop = NULL;
 IShellFolder* pSub = NULL;
 IExtractImage* pIExtract = NULL;
 LPITEMIDLIST pList = NULL;
 HBITMAP   hBmp = NULL;

 // get the desktop directory
 if (SUCCEEDED(SHGetDesktopFolder(&pDesktop)))
 {
  // get the pidl for the directory
  HRESULT hr = pDesktop->ParseDisplayName(NULL, NULL, wDirName, NULL, &pList, NULL);
  if (FAILED(hr))
  { 
   throw new CUserInterfaceException(”Failed to parse the directory name”);
  }

  // get the directory IShellFolder interface
  hr = pDesktop->BindToObject(pList, NULL, IID_IShellFolder, (void**)&pSub);
  if (FAILED(hr))
  {
   throw new CUserInterfaceException(”Failed to bind to the directory”);
  }

  // get the file’s pidl
  hr = pSub->ParseDisplayName(NULL, NULL, wFileName, NULL, &pList, NULL);
  if (FAILED(hr))
  {
   throw new CUserInterfaceException(”Failed to parse the file name”);
  }

  // get the IExtractImage interface
  LPCITEMIDLIST pidl = pList;
  hr = pSub->GetUIObjectOf(NULL, 1, &pidl, IID_IExtractImage, NULL, (void**)&pIExtract);
  
  // set our desired image size
  SIZE size;
  size.cx = longestEdge;
  size.cy = longestEdge;     
  
  if(pIExtract == NULL)
  {
   return NULL;
  }        

  // The IEIFLAG_ORIGSIZE flag tells it to use the original aspect
  // ratio for the image size. The IEIFLAG_QUALITY flag tells the
  // interface we want the image to be the best possible quality.
  DWORD dwFlags = IEIFLAG_ORIGSIZE | IEIFLAG_QUALITY;     
  
  OLECHAR pathBuffer[MAX_PATH];
  hr = pIExtract->GetLocation(pathBuffer, MAX_PATH, NULL, &size, colorDepth, &dwFlags);        
  if (FAILED(hr))
  {
   throw new CUserInterfaceException(”The call to GetLocation failed”);
  }

  hr = pIExtract->Extract(&hBmp);  //THIS IS WHERE I GET THE ERROR MESSAGE

  pIExtract->Release();
 } // if

 // Release the COM objects we have a reference to.
 pDesktop->Release();
 pSub->Release();

 return hBmp;
}