这里是一些如何得到Office缩略图的步骤：
- 创建一个新的文档，文档可以为任意类型(docx, xlsx, pptx等类型都可以)。
- 保存文档，这里必须注意将"Save Thumbnail"勾上，否则不能产生缩略图效果。
- 接下来将API封装成一个类，方便使用。
using System; using System.Diagnostics; using System.Drawing; using System.IO; using System.Runtime.InteropServices; using System.Text; public class ShellThumbnail : IDisposable { [Flags] private enum ESTRRET { STRRET_WSTR = 0, STRRET_OFFSET = 1, STRRET_CSTR = 2 } [Flags] private enum ESHCONTF { SHCONTF_FOLDERS = 32, SHCONTF_NONFOLDERS = 64, SHCONTF_INCLUDEHIDDEN = 128, } [Flags] private enum ESHGDN { SHGDN_NORMAL = 0, SHGDN_INFOLDER = 1, SHGDN_FORADDRESSBAR = 16384, SHGDN_FORPARSING = 32768 } [Flags] private enum ESFGAO { SFGAO_CANCOPY = 1, SFGAO_CANMOVE = 2, SFGAO_CANLINK = 4, SFGAO_CANRENAME = 16, SFGAO_CANDELETE = 32, SFGAO_HASPROPSHEET = 64, SFGAO_DROPTARGET = 256, SFGAO_CAPABILITYMASK = 375, SFGAO_LINK = 65536, SFGAO_SHARE = 131072, SFGAO_READONLY = 262144, SFGAO_GHOSTED = 524288, SFGAO_DISPLAYATTRMASK = 983040, SFGAO_FILESYSANCESTOR = 268435456, SFGAO_FOLDER = 536870912, SFGAO_FILESYSTEM = 1073741824, SFGAO_HASSUBFOLDER = -2147483648, SFGAO_CONTENTSMASK = -2147483648, SFGAO_VALIDATE = 16777216, SFGAO_REMOVABLE = 33554432, SFGAO_COMPRESSED = 67108864, } private enum EIEIFLAG { IEIFLAG_ASYNC = 1, IEIFLAG_CACHE = 2, IEIFLAG_ASPECT = 4, IEIFLAG_OFFLINE = 8, IEIFLAG_GLEAM = 16, IEIFLAG_SCREEN = 32, IEIFLAG_ORIGSIZE = 64, IEIFLAG_NOSTAMP = 128, IEIFLAG_NOBORDER = 256, IEIFLAG_QUALITY = 512 } [StructLayout(LayoutKind.Sequential, Pack = 4, Size = 0, CharSet = CharSet.Auto)] private struct STRRET_CSTR { public ESTRRET uType; [MarshalAs(UnmanagedType.ByValArray, SizeConst = 520)] public byte[] cStr; } [StructLayout(LayoutKind.Explicit, CharSet = CharSet.Auto)] private struct STRRET_ANY { [FieldOffset(0)] public ESTRRET uType; [FieldOffset(4)] public IntPtr pOLEString; } [StructLayoutAttribute(LayoutKind.Sequential)] private struct SIZE { public int cx; public int cy; } [ComImport(), Guid("00000000-0000-0000-C000-000000000046")] [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] private interface IUnknown { [PreserveSig()] IntPtr QueryInterface(ref Guid riid, ref IntPtr pVoid); [PreserveSig()] IntPtr AddRef(); [PreserveSig()] IntPtr Release(); } [ComImportAttribute()] [GuidAttribute("00000002-0000-0000-C000-000000000046")] [InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)] private interface IMalloc { [PreserveSig()] IntPtr Alloc(int cb); [PreserveSig()] IntPtr Realloc(IntPtr pv, int cb); [PreserveSig()] void Free(IntPtr pv); [PreserveSig()] int GetSize(IntPtr pv); [PreserveSig()] int DidAlloc(IntPtr pv); [PreserveSig()] void HeapMinimize(); } [ComImportAttribute()] [GuidAttribute("000214F2-0000-0000-C000-000000000046")] [InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)] private interface IEnumIDList { [PreserveSig()] int Next(int celt, ref IntPtr rgelt, ref int pceltFetched); void Skip(int celt); void Reset(); void Clone(ref IEnumIDList ppenum); } [ComImportAttribute()] [GuidAttribute("000214E6-0000-0000-C000-000000000046")] [InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)] private interface IShellFolder { void ParseDisplayName(IntPtr hwndOwner, IntPtr pbcReserved, [MarshalAs(UnmanagedType.LPWStr)]string lpszDisplayName, ref int pchEaten, ref IntPtr ppidl, ref int pdwAttributes); void EnumObjects(IntPtr hwndOwner, [MarshalAs(UnmanagedType.U4)]ESHCONTF grfFlags, ref IEnumIDList ppenumIDList); void BindToObject(IntPtr pidl, IntPtr pbcReserved, ref Guid riid, ref IShellFolder ppvOut); void BindToStorage(IntPtr pidl, IntPtr pbcReserved, ref Guid riid, IntPtr ppvObj); [PreserveSig()] int CompareIDs(IntPtr lParam, IntPtr pidl1, IntPtr pidl2); void CreateViewObject(IntPtr hwndOwner, ref Guid riid, IntPtr ppvOut); void GetAttributesOf(int cidl, IntPtr apidl, [MarshalAs(UnmanagedType.U4)]ref ESFGAO rgfInOut); void GetUIObjectOf(IntPtr hwndOwner, int cidl, ref IntPtr apidl, ref Guid riid, ref int prgfInOut, ref IUnknown ppvOut); void GetDisplayNameOf(IntPtr pidl, [MarshalAs(UnmanagedType.U4)]ESHGDN uFlags, ref STRRET_CSTR lpName); void SetNameOf(IntPtr hwndOwner, IntPtr pidl, [MarshalAs(UnmanagedType.LPWStr)]string lpszName, [MarshalAs(UnmanagedType.U4)] ESHCONTF uFlags, ref IntPtr ppidlOut); } [ComImportAttribute(), GuidAttribute("BB2E617C-0920-11d1-9A0B-00C04FC2D6C1"), InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)] private interface IExtractImage { void GetLocation([Out(), MarshalAs(UnmanagedType.LPWStr)] StringBuilder pszPathBuffer, int cch, ref int pdwPriority, ref SIZE prgSize, int dwRecClrDepth, ref int pdwFlags); void Extract(ref IntPtr phBmpThumbnail); } private class UnmanagedMethods { [DllImport("shell32", CharSet = CharSet.Auto)] internal extern static int SHGetMalloc(ref IMalloc ppMalloc); [DllImport("shell32", CharSet = CharSet.Auto)] internal extern static int SHGetDesktopFolder(ref IShellFolder ppshf); [DllImport("shell32", CharSet = CharSet.Auto)] internal extern static int SHGetPathFromIDList(IntPtr pidl, StringBuilder pszPath); [DllImport("gdi32", CharSet = CharSet.Auto)] internal extern static int DeleteObject(IntPtr hObject); } ~ShellThumbnail() { Dispose(); } private IMalloc alloc = null; private bool disposed = false; private Size _desiredSize = new Size(100, 100); private Bitmap _thumbNail; public Bitmap ThumbNail { get { return _thumbNail; } } public Size DesiredSize { get { return _desiredSize; } set { _desiredSize = value; } } private IMalloc Allocator { get { if (!disposed) { if (alloc == null) { UnmanagedMethods.SHGetMalloc(ref alloc); } } else { Debug.Assert(false, "Object has been disposed."); } return alloc; } } public Bitmap GetThumbnail(string fileName) { if (!File.Exists(fileName) && !Directory.Exists(fileName)) { throw new FileNotFoundException(string.Format("The file '{0}' does not exist", fileName), fileName); } if (_thumbNail != null) { _thumbNail.Dispose(); _thumbNail = null; } IShellFolder folder = null; try { folder = getDesktopFolder; } catch (Exception ex) { throw ex; } if (folder != null) { IntPtr pidlMain = IntPtr.Zero; try { int cParsed = 0; int pdwAttrib = 0; string filePath = Path.GetDirectoryName(fileName); folder.ParseDisplayName(IntPtr.Zero, IntPtr.Zero, filePath, ref cParsed, ref pidlMain, ref pdwAttrib); } catch (Exception ex) { Marshal.ReleaseComObject(folder); throw ex; } if (pidlMain != IntPtr.Zero) { Guid iidShellFolder = new Guid("000214E6-0000-0000-C000-000000000046"); IShellFolder item = null; try { folder.BindToObject(pidlMain, IntPtr.Zero, ref iidShellFolder, ref item); } catch (Exception ex) { Marshal.ReleaseComObject(folder); Allocator.Free(pidlMain); throw ex; } if (item != null) { IEnumIDList idEnum = null; try { item.EnumObjects(IntPtr.Zero, (ESHCONTF.SHCONTF_FOLDERS | ESHCONTF.SHCONTF_NONFOLDERS), ref idEnum); } catch (Exception ex) { Marshal.ReleaseComObject(folder); Allocator.Free(pidlMain); throw ex; } if (idEnum != null) { int hRes = 0; IntPtr pidl = IntPtr.Zero; int fetched = 0; bool complete = false; while (!complete) { hRes = idEnum.Next(1, ref pidl, ref fetched); if (hRes != 0) { pidl = IntPtr.Zero; complete = true; } else { if (_getThumbNail(fileName, pidl, item)) { complete = true; } } if (pidl != IntPtr.Zero) { Allocator.Free(pidl); } } Marshal.ReleaseComObject(idEnum); } Marshal.ReleaseComObject(item); } Allocator.Free(pidlMain); } Marshal.ReleaseComObject(folder); } return ThumbNail; } private bool _getThumbNail(string file, IntPtr pidl, IShellFolder item) { IntPtr hBmp = IntPtr.Zero; IExtractImage extractImage = null; try { string pidlPath = PathFromPidl(pidl); if (Path.GetFileName(pidlPath).ToUpper().Equals(Path.GetFileName(file).ToUpper())) { IUnknown iunk = null; int prgf = 0; Guid iidExtractImage = new Guid("BB2E617C-0920-11d1-9A0B-00C04FC2D6C1"); item.GetUIObjectOf(IntPtr.Zero, 1, ref pidl, ref iidExtractImage, ref prgf, ref iunk); extractImage = (IExtractImage)iunk; if (extractImage != null) { Console.WriteLine("Got an IExtractImage object!"); SIZE sz = new SIZE(); sz.cx = DesiredSize.Width; sz.cy = DesiredSize.Height; StringBuilder location = new StringBuilder(260, 260); int priority = 0; int requestedColourDepth = 32; EIEIFLAG flags = EIEIFLAG.IEIFLAG_ASPECT | EIEIFLAG.IEIFLAG_SCREEN; int uFlags = (int)flags; extractImage.GetLocation(location, location.Capacity, ref priority, ref sz, requestedColourDepth, ref uFlags); extractImage.Extract(ref hBmp); if (hBmp != IntPtr.Zero) { _thumbNail = Bitmap.FromHbitmap(hBmp); } Marshal.ReleaseComObject(extractImage); extractImage = null; } return true; } else { return false; } } catch (Exception ex) { if (hBmp != IntPtr.Zero) { UnmanagedMethods.DeleteObject(hBmp); } if (extractImage != null) { Marshal.ReleaseComObject(extractImage); } throw ex; } } private string PathFromPidl(IntPtr pidl) { StringBuilder path = new StringBuilder(260, 260); int result = UnmanagedMethods.SHGetPathFromIDList(pidl, path); if (result == 0) { return string.Empty; } else { return path.ToString(); } } private IShellFolder getDesktopFolder { get { IShellFolder ppshf = null; int r = UnmanagedMethods.SHGetDesktopFolder(ref ppshf); return ppshf; } } public void Dispose() { if (!disposed) { if (alloc != null) { Marshal.ReleaseComObject(alloc); } alloc = null; if (_thumbNail != null) { _thumbNail.Dispose(); } disposed = true; } } } - 最后就可以通过这个类生成缩略图了。
protected void Page_Load(object sender, EventArgs e) { var thumbnail = new ShellThumbnail(); thumbnail.GetThumbnail(Page.MapPath("your file name.xlsx")); var image = thumbnail.ThumbNail; image.Save(@"C:\thumbnail name.png", System.Drawing.Imaging.ImageFormat.Png); thumbnail.Dispose(); }
值得注意的就是如果在新建文档的时候没有选择"Save Thumbnail"的话，结果是不能得到这个文档的缩略图的。原因？很简单，Office文档在保存的时候会自动截取一张图片，这张图片就是缩略图，而刚刚用到的API就是把这张图片取出来。
如果文档默认没有生成缩略图，extractImage.Extract(ref hBmp)这里会报异常，因此，在实际开发中捕获这个异常并做相应的处理就好了。我居然还花了些时间去确认引起这个异常的原因，浪费时间了啊=.=!