在HttpHandler中通过Windows API生成图像的Thumnail

我使用下面的代码在ASP.Net应用程序中创建一个Image的缩略图。

using System; using System.Diagnostics; using System.Drawing; using System.IO; using System.Runtime.InteropServices; using System.Text; namespace RMA.Shell { 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 (string.IsNullOrEmpty(fileName)) return null; 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; try { extractImage.GetLocation(location, location.Capacity, ref priority, ref sz, requestedColourDepth, ref uFlags); extractImage.Extract(ref hBmp); } catch (System.Runtime.InteropServices.COMException ex) { } 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; } } } } 

我已经创建了一个http处理程序，我从这里调用了GetThumbnail（）方法

 using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Drawing; using System.IO; using RMA.Shell; using System.Drawing.Imaging; namespace DemoApp { /// 
 /// Summary description for ImageHandler /// 
 public class ImageHandler : IHttpHandler { public void ProcessRequest(HttpContext context) { byte[] buffer = null; string imgUrl = context.Request.Params["url"].ToString(); if (!string.IsNullOrEmpty(imgUrl)) { ShellThumbnail thumb = new ShellThumbnail(); Bitmap bmp = thumb.GetThumbnail(context.Server.MapPath(imgUrl)); using (MemoryStream stram = new MemoryStream()) { bmp.Save(stram, ImageFormat.Jpeg); buffer = stram.ToArray(); bmp.Dispose(); thumb.Dispose(); } HttpCachePolicy cachePilicy = context.Response.Cache; cachePilicy.SetAllowResponseInBrowserHistory(false); cachePilicy.SetCacheability(HttpCacheability.NoCache); cachePilicy.SetExpires(DateTime.Now.AddDays(-1)); context.Response.Clear(); context.Response.ContentType = "Image/jpeg"; context.Response.OutputStream.Write(buffer, 0, buffer.Length); buffer = null; context.Response.OutputStream.Close(); context.Response.End(); } } public bool IsReusable { get { return true; } } } } 

我对这段代码有些怀疑

1. 这个GetThumbnail（）方法如何工作？ 它是否使用windows thumnail cache ie.thumb.db？ 或者它为每次通话产生thumnail？
2. 使用此COM API有任何性能问题吗？ 它适用于多个并发的http请求吗？

3.这与Windows API代码包Shell实现有什么区别，例如

 ShellFile shellFile = ShellFile.FromFilePath(pathToYourFile); Bitmap shellThumb = shellFile.Thumbnail.ExtraLargeBitmap; 

哪一个是更好的选择？

4.内部实施是什么？ 是使用GDI +还是其他任何方法，如IPP？

请澄清

Answer 1

当有简单而干净的托管解决方案用于调整图像大小时，不明白为什么要干掉COM乱七八糟的东西：

1. Image.GetThumbnailImage – 此方法的缺点是重新resize的图像质量低

2. ImageResizer – 开源图像大小调整组件，非常好的缩略图质量