因为用shell取缩略图时，对于损坏的文件，读出来的图有黑边，所以就诞生了以下方法，不过这个效率要比用shell取的低3-4倍（耗时主要是在将黑色背景转为透明的过程）。

1.添加类WindowsThumbnailProvider

[csharp] view plain copy

  1. [Flags]
  2. public enum ThumbnailOptions
  3. {
  4. None = 0x00,
  5. BiggerSizeOk = 0x01,
  6. InMemoryOnly = 0x02,
  7. IconOnly = 0x04,
  8. ThumbnailOnly = 0x08,
  9. InCacheOnly = 0x10,
  10. }
  12. public class WindowsThumbnailProvider
  13. {
  14. private const string IShellItem2Guid = "7E9FB0D3-919F-4307-AB2E-9B1860310C93";
  16. [dllImport("shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
  17. internal static extern int SHCreateItemFromParsingName(
  18. [MarshalAs(UnmanagedType.LPWStr)] string path,
  19. // The following parameter is not used - binding context.
  20. IntPtr pbc,
  21. ref Guid riid,
  22. [MarshalAs(UnmanagedType.Interface)] out IShellItem shellItem);
  24. [DllImport("gdi32.dll")]
  25. [return: MarshalAs(UnmanagedType.Bool)]
  26. internal static extern bool DeleteObject(IntPtr hObject);
  28. [ComImport]
  29. [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
  30. [Guid("43826d1e-e718-42ee-bc55-a1e261c37bfe")]
  31. internal interface IShellItem
  32. {
  33. void BindToHandler(IntPtr pbc,
  34. [MarshalAs(UnmanagedType.LPStruct)]Guid bhid,
  35. [MarshalAs(UnmanagedType.LPStruct)]Guid riid,
  36. out IntPtr ppv);
  38. void GetParent(out IShellItem ppsi);
  39. void GetDisplayName(SIGDN sigdnName, out IntPtr ppszName);
  40. void GetAttributes(uint sfgaoMask, out uint psfgaoAttribs);
  41. void Compare(IShellItem psi, uint hint, out int piOrder);
  42. };
  44. internal enum SIGDN : uint
  45. {
  46. NORMALDISPLAY = 0,
  47. PARENTRELATIVEPARSING = 0x80018001,
  48. PARENTRELATIVEFORADDRESSBAR = 0x8001c001,
  49. DESKTOPABSOLUTEPARSING = 0x80028000,
  50. PARENTRELATIVEEDITING = 0x80031001,
  51. DESKTOPABSOLUTEEDITING = 0x8004c000,
  52. FILESYSPATH = 0x80058000,
  53. URL = 0x80068000
  54. }
  56. internal enum HResult
  57. {
  58. Ok = 0x0000,
  59. False = 0x0001,
  60. InvalidArguments = unchecked((int)0x80070057),
  61. OutOfMemory = unchecked((int)0x8007000E),
  62. NoInterface = unchecked((int)0x80004002),
  63. Fail = unchecked((int)0x80004005),
  64. ElementNotFound = unchecked((int)0x80070490),
  65. TypeElementNotFound = unchecked((int)0x8002802B),
  66. NoObject = unchecked((int)0x800401E5),
  67. Win32ErrorCanceled = 1223,
  68. Canceled = unchecked((int)0x800704C7),
  69. ResourceInUse = unchecked((int)0x800700AA),
  70. AccessDenied = unchecked((int)0x80030005)
  71. }
  73. [ComImportAttribute()]
  74. [GuidAttribute("bcc18b79-ba16-442f-80c4-8a59c30c463b")]
  75. [InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
  76. internal interface IShellItemImageFactory
  77. {
  78. [PreserveSig]
  79. HResult GetImage(
  80. [In, MarshalAs(UnmanagedType.Struct)] NativeSize size,
  81. [In] ThumbnailOptions flags,
  82. [Out] out IntPtr phbm);
  83. }
  85. [StructLayout(LayoutKind.Sequential)]
  86. internal struct NativeSize
  87. {
  88. private int width;
  89. private int height;
  91. public int Width { set { width = value; } }
  92. public int Height { set { height = value; } }
  93. };
  95. [StructLayout(LayoutKind.Sequential)]
  96. public struct RGBQUAD
  97. {
  98. public byte rgbBlue;
  99. public byte rgbGreen;
  100. public byte rgbRed;
  101. public byte rgbReserved;
  102. }
  104. public static Bitmap GetThumbnail(string fileName, int width, int height, ThumbnailOptions options)
  105. {
  106. IntPtr hBitmap = GetHBitmap(Path.GetFullPath(fileName), width, height, options);
  108. try
  109. {
  110. // return a System.Drawing.Bitmap from the hBitmap
  111. return GetBitmapFromHBitmap(hBitmap);
  112. }
  113. finally
  114. {
  115. // delete HBitmap to avoid memory leaks
  116. DeleteObject(hBitmap);
  117. }
  118. }
  120. public static Bitmap GetBitmapFromHBitmap(IntPtr nativeHBitmap)
  121. {
  122. Bitmap bmp = Bitmap.FromHbitmap(nativeHBitmap);
  124. if (Bitmap.GetPixelFormatSize(bmp.PixelFormat) < 32)
  125. return bmp;
  127. return CreateAlphaBitmap(bmp, PixelFormat.Format32bppArgb);
  128. }
  130. public static Bitmap CreateAlphaBitmap(Bitmap srcBitmap, PixelFormat targetPixelFormat)
  131. {
  132. Bitmap result = new Bitmap(srcBitmap.Width, srcBitmap.Height, targetPixelFormat);
  134. Rectangle bmpBounds = new Rectangle(0, 0, srcBitmap.Width, srcBitmap.Height);
  136. BitmapData srcData = srcBitmap.LockBits(bmpBounds, ImageLockMode.ReadOnly, srcBitmap.PixelFormat);
  138. bool isAlplaBitmap = false;
  140. try
  141. {
  142. for (int y = 0; y <= srcData.Height - 1; y )
  143. {
  144. for (int x = 0; x <= srcData.Width - 1; x )
  145. {
  146. Color pixelColor = Color.FromArgb(
  147. Marshal.ReadInt32(srcData.Scan0, (srcData.Stride * y) (4 * x)));
  149. if (pixelColor.A > 0 & pixelColor.A < 255)
  150. {
  151. isAlplaBitmap = true;
  152. }
  154. result.SetPixel(x, y, pixelColor);
  155. }
  156. }
  157. }
  158. finally
  159. {
  160. srcBitmap.UnlockBits(srcData);
  161. }
  163. if (isAlplaBitmap)
  164. {
  165. return result;
  166. }
  167. else
  168. {
  169. return srcBitmap;
  170. }
  171. }
  173. private static IntPtr GetHBitmap(string fileName, int width, int height, ThumbnailOptions options)
  174. {
  175. IShellItem nativeShellItem;
  176. Guid shellItem2Guid = new Guid(IShellItem2Guid);
  177. int retCode = SHCreateItemFromParsingName(fileName, IntPtr.Zero, ref shellItem2Guid, out nativeShellItem);
  179. if (retCode != 0)
  180. throw Marshal.GetExceptionForHR(retCode);
  182. NativeSize nativeSize = new NativeSize();
  183. nativeSize.Width = width;
  184. nativeSize.Height = height;
  186. IntPtr hBitmap;
  187. HResult hr = ((IShellItemImageFactory)nativeShellItem).GetImage(nativeSize, options, out hBitmap);
  189. Marshal.ReleaseComObject(nativeShellItem);
  191. if (hr == HResult.Ok) return hBitmap;
  193. throw Marshal.GetExceptionForHR((int)hr);
  194. }
  195. }

2.使用方法：[csharp] view plain copy

  1. int pic_size = 256;
  3. Bitmap bm = WindowsThumbnailProvider.GetThumbnail(path, pic_size, pic_size, ThumbnailOptions.None);

c语言获得当前文件指针位置（语言获取任意文件的缩略图）(1)

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