C # 通过 windows api 从文件中获取缩略图

Not exactly what you asked, but here's a project to open a Thumbs.db file.
The Wikipedia article has more information on where to find thumbnails in Vista & 7.

Here's the code to get the image:

public byte[] GetThumbData(string filename)
{
IStorageWrapper wrapper = new IStorageWrapper(_thumbDBFile, false);
foreach(CatalogItem catItem in _catalogItems)
{
if (catItem.filename == filename)
{
string streamName = BuildReverseString(catItem.itemID);
FileObject fileObject = wrapper.OpenUCOMStream(null, streamName);
byte[] rawJPGData = new byte [fileObject.Length];
fileObject.Read(rawJPGData, 0, (int)fileObject.Length);
fileObject.Close();


// 3 ints of header data need to be removed
// Don't know what first int is.
// 2nd int is thumb index
// 3rd is size of thumbnail data.
byte[] jpgData = new byte[rawJPGData.Length - 12];
for (int index = 12; index < jpgData.Length; index++)
{
jpgData[index - 12] = rawJPGData[index];
}
return jpgData;
}
}
return null;
}


public Image GetThumbnailImage(string filename)
{
byte[] thumbData = GetThumbData(filename);
if (null == thumbData)
{
return null;
}
MemoryStream ms = new MemoryStream(thumbData);
Image img = Image.FromStream(ms);
return img;
}

Here's a class that I found searching around the internet. It looks like the original code came from http://www.experts-exchange.com/Programming/Languages/C_Sharp/Q_21789724.html, but I can't see it to give proper attribution. I found the source here: http://www.vbforums.com/showthread.php?t=527704

Here's a class with the proper COM calls, reproduced here for posterity:

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;
}
}
}
}

Ran across this today -- it's a few months old, but it got the job done for me (on Win7, extracting thumbnails on MPEG-4 files):

• Source : https://github.com/dbarros/WindowsAPICodePack
• Nuget : https://www.nuget.org/packages/WindowsAPICodePack-Shell

Code:

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

Hope it helps!

Microsoft Office Thumbnails in SharePoint at http://msdn.microsoft.com/en-us/library/aa289172(VS.71).aspx. is exactly what you want. (I had no trouble converting the VB.NET code into C# using http://www.developerfusion.com/tools/convert/vb-to-csharp/.)

Regarding the code you posted in your answer, Thumbnail Extraction Using the Shell at http://www.vbaccelerator.com/home/net/code/libraries/Shell_Projects/Thumbnail_Extraction/article.asp is the original article the code is from. I believe nearly all IExtractImage samples (you find searching) are based on this article's code, due to naming convention, comments, and so on, that are carried from the original. Since this article dates from April 2003, it carries some non-standard (non-.NET) coding conventions. I did some basic testing, and there are garbage collection issues, freeing unmanaged resource issues, and other clean-up issues. Therefore, I make a strong recommendation to avoid the code in that article. Moreover, the code is structured is such a way to make maintenance difficult.

There is a clean simplier version on MSDN, dated July 2005, called Microsoft Office Thumbnails in SharePoint at http://msdn.microsoft.com/en-us/library/aa289172(VS.71).aspx. This code and the article's code share similarities, which leads me to believe the Thumbnail Extraction Using the Shell article is the basis for the longestEdge0 article. The VB.NET version of GetThumbnailImage ignores the longestEdge parameter, but the C++ version uses it and documents the use of the ORIGSIZE and QUALITY flags. In addition, the code illustrates how to use .NET's FreeCoTaskMem instead of the Shell's IMalloc and SHGetMalloc.

IExtractImage works with files, folders, and other namespace objects. The MSDN code works with hidden files, whereas, the vbAccelerator code needs then SHCONTF_INCLUDEHIDDEN added to the EnumObjects call. In addition, the vbAccelerator enumerates over the shell folder's objects looking for the specified file, which seems a waste of time. This may have been needed to find the correct "relative" PIDL that is used for the GetUIObjectOf call.

ShellThumbnail (Work-In-Progress)

Complete sample project at http://cid-7178d2c79ba0a7e3.office.live.com/self.aspx/.Public/ShellThumbnail.zip.

Imports System.Runtime.InteropServices


Namespace Shell


''' <summary>
''' Generates a thumbnail of a folder's picture or a file's image.
''' </summary>
''' <remarks>This is the "Folder's Picture" and not the "Folder's Icon"! Use SHGetFileInfo to generate the thumbnail for a folder's icon or for a file that does not have a thumbnail handler.</remarks>
''' <reference>Microsoft Office Thumbnails in SharePoint at http://msdn.microsoft.com/en-us/library/aa289172%28VS.71%29.aspx.</reference>
Public Class ShellThumbnail


'TODO - Work out the details for image size and IEIFLAG handling.


#Region " Determining Thumbnail Size and Quality [documentation] "


'http://support.microsoft.com/kb/835823
'Determining Thumbnail Size and Quality
'Browse to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer. Create or modify two DWORDs called ThumbnailSize and ThumbnailQuality. For ThumbnailSize set the value in pixels, with the default being 96. For ThumbnailQuality set the value as a number that represents the percentage quality between 50 and 100.




'http://www.pctools.com/guides/registry/detail/1066/ (modified)
'  User Key: [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer]
'System Key: [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer]
'Value Name: ThumbnailSize, ThumbnailQuality
' Data Type: REG_DWORD (DWORD Value)
'Value Data: Size in pixels (32-255), Quality Percentage (50-100)




'Microsoft® Windows® XP Registry Guide
'Jerry Honeycutt
'09/11/2002
'Microsoft Press
'http://www.microsoft.com/mspress/books/sampchap/6232.aspx#118
'<H3><I><A name=118></A>Thumbnails</I></H3>The Thumbnails category controls the
'quality of thumbnails in Windows Explorer. Table 5-10 describes the values for
'Image Quality and Size. Create values that you don't see in the registry. The
'default value for <CODE>ThumbnailQuality</CODE> is <CODE>0x5A</CODE>. The
'default value for <CODE>ThumbnailSize</CODE> is <CODE>0x60</CODE>. Keep in mind
'that higher quality and larger thumbnails require more disk space, which is not
'usually a problem, but they also take longer to display. Changing the quality
'does not affect thumbnails that already exist on the file system.
'<P><B>Table 5-10 </B><I>Values in Thumbnails</I>
'<P>
'<TABLE border=0 cellSpacing=1 cellPadding=4 width="100%">
'<TBODY>
'<TR>
'<TD bgColor=#999999 vAlign=top><B>Setting</B></TD>
'<TD bgColor=#999999 vAlign=top><B>Name</B></TD>
'<TD bgColor=#999999 vAlign=top><B>Type</B></TD>
'<TD bgColor=#999999 vAlign=top><B>Data</B></TD></TR>
'<TR>
'<TD bgColor=#cccccc
'vAlign=top><CODE><B>HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer</B></CODE></TD>
'<TD bgColor=#cccccc vAlign=top> </TD>
'<TD bgColor=#cccccc vAlign=top> </TD>
'<TD bgColor=#cccccc vAlign=top> </TD></TR>
'<TR>
'<TD bgColor=#cccccc vAlign=top><CODE>Image Quality</CODE></TD>
'<TD bgColor=#cccccc vAlign=top><CODE>ThumbnailQuality</CODE></TD>
'<TD bgColor=#cccccc vAlign=top><CODE>REG_DWORD</CODE></TD>
'<TD bgColor=#cccccc vAlign=top><CODE>0x32 - 0x64</CODE></TD></TR>
'<TR>
'<TD bgColor=#cccccc vAlign=top><CODE>Size (pixels)</CODE></TD>
'<TD bgColor=#cccccc vAlign=top><CODE>ThumbnailSize</CODE></TD>
'<TD bgColor=#cccccc vAlign=top><CODE>REG_DWORD</CODE></TD>
'<TD bgColor=#cccccc vAlign=top><CODE>0x20 - 0xFF</CODE></TD></TR></TBODY></TABLE></P>


#End Region


Public Shared ReadOnly DefaultThumbnailSize As New System.Drawing.Size(96, 96)


Public Const DefaultColorDepth As Integer = 32


''' <summary>
''' Used to request an image from an object, such as an item in a Shell folder.
''' </summary>
''' <param name="path">An absolute path to a file or folder.</param>
Public Shared Function ExtractImage(ByVal path As String) As Bitmap
Return ExtractImage(path, System.Drawing.Size.Empty, DefaultColorDepth, 0)
End Function


''' <summary>
''' Used to request an image from an object, such as an item in a Shell folder.
''' </summary>
''' <param name="path">An absolute path to a file or folder.</param>
''' <param name="size"></param>
Public Shared Function ExtractImage(ByVal path As String, ByVal size As System.Drawing.Size) As Bitmap
Return ExtractImage(path, size, DefaultColorDepth, 0)
End Function


''' <summary>
''' Used to request an image from an object, such as an item in a Shell folder.
''' </summary>
''' <param name="path">An absolute path to a file or folder.</param>
''' <param name="size"></param>
''' <param name="recommendedColorDepth">The recommended color depth in units of bits per pixel. The default is 32.</param>
Public Shared Function ExtractImage(ByVal path As String, ByVal size As System.Drawing.Size, ByVal recommendedColorDepth As Integer) As Bitmap
Return ExtractImage(path, size, recommendedColorDepth, 0)
End Function


''' <summary>
''' Used to request an image from an object, such as an item in a Shell folder.
''' </summary>
''' <param name="path">An absolute path to a file or folder.</param>
''' <param name="size"></param>
''' <param name="recommendedColorDepth">The recommended color depth in units of bits per pixel. The default is 32.</param>
Private Shared Function ExtractImage(ByVal path As String, ByVal size As System.Drawing.Size, ByVal recommendedColorDepth As Integer, ByVal flags As IEIFLAG) As Bitmap
Dim oResult As Bitmap = Nothing


Dim oDesktopFolder As IShellFolder = Nothing
Dim hParentIDL As IntPtr
Dim hIDL As IntPtr


Dim oParentFolder As IShellFolder
Dim hParentFolder As IntPtr
Dim oExtractImage As IExtractImage
Dim hExtractImage As IntPtr


'Divide the file name into a path and file/folder name.
Dim sFolderName As String = System.IO.Path.GetDirectoryName(path)
Dim sBaseName As String = System.IO.Path.GetFileName(path)


'Get the desktop IShellFolder.
If SHGetDesktopFolder(oDesktopFolder) <> Missico.Win32.S_OK Then
Throw New System.Runtime.InteropServices.COMException
End If


'Get the parent folder for the specified path.
oDesktopFolder.ParseDisplayName(IntPtr.Zero, IntPtr.Zero, sFolderName, 0, hParentIDL, 0)
oDesktopFolder.BindToObject(hParentIDL, IntPtr.Zero, ShellGUIDs.IID_IShellFolder, hParentFolder)
oParentFolder = CType(Marshal.GetTypedObjectForIUnknown(hParentFolder, GetType(IShellFolder)), IShellFolder)


'Get the file/folder's IExtractImage
oParentFolder.ParseDisplayName(IntPtr.Zero, IntPtr.Zero, sBaseName, 0, hIDL, 0)
oParentFolder.GetUIObjectOf(IntPtr.Zero, 1, New IntPtr() {hIDL}, ShellGUIDs.IID_IExtractImage, IntPtr.Zero, hExtractImage)


'Free the pidls. The Runtime Callable Wrappers (RCW) should automatically release the COM objects.
Marshal.FreeCoTaskMem(hParentIDL)
Marshal.FreeCoTaskMem(hIDL)


Marshal.FinalReleaseComObject(oParentFolder)
Marshal.FinalReleaseComObject(oDesktopFolder)


If hExtractImage = IntPtr.Zero Then


'There is no handler for this file, which is odd. I believe we should default the file's type icon.
Debug.WriteLine(String.Format("There is no thumbnail for the specified file '{0}'.", path), "ShellThumbnail.ExtractImage")


Else


oExtractImage = CType(Marshal.GetTypedObjectForIUnknown(hExtractImage, GetType(IExtractImage)), IExtractImage)


'Set the size and flags
Dim oSize As Missico.Win32.SIZE 'must specify a size
Dim iFlags As IEIFLAG = flags Or IEIFLAG.IEIFLAG_ORIGSIZE Or IEIFLAG.IEIFLAG_QUALITY Or IEIFLAG.IEIFLAG_ASPECT


If size.IsEmpty Then


oSize.cx = DefaultThumbnailSize.Width
oSize.cy = DefaultThumbnailSize.Height


Else


oSize.cx = size.Width
oSize.cy = size.Height


End If




Dim hBitmap As IntPtr
Dim sPath As New System.Text.StringBuilder(Missico.Win32.MAX_PATH, Missico.Win32.MAX_PATH)




oExtractImage.GetLocation(sPath, sPath.Capacity, 0, oSize, recommendedColorDepth, iFlags)


'if the specified path is to a folder then IExtractImage.Extract fails.


Try


oExtractImage.Extract(hBitmap)


Catch ex As System.Runtime.InteropServices.COMException


'clear the handle since extract failed
hBitmap = IntPtr.Zero


Debug.WriteLine(String.Format("There is no thumbnail for the specified folder '{0}'.", path), "ShellThumbnail.ExtractImage")


Finally


Marshal.FinalReleaseComObject(oExtractImage)


End Try


If Not hBitmap.Equals(IntPtr.Zero) Then


'create the image from the handle
oResult = System.Drawing.Bitmap.FromHbitmap(hBitmap)


'dump the properties to determine what kind of bitmap is returned
'Missico.Diagnostics.ObjectDumper.Write(oResult)


'Tag={ }
'PhysicalDimension={Width=96, Height=96}
'Size={Width=96, Height=96}
'Width=96
'Height=96
'HorizontalResolution=96
'VerticalResolution=96
'Flags=335888
'RawFormat={ }
'PixelFormat=Format32bppRgb
'Palette={ }
'FrameDimensionsList=...
'PropertyIdList=...
'PropertyItems=...


Missico.Win32.DeleteObject(hBitmap) 'release the handle


End If


End If


Return oResult
End Function


End Class


End Namespace

Thanks to @Christian Nunciato, I want to explain more:

After you install WindowsAPICodePack-Shell by typing following command in Nuget console:

Install-Package WindowsAPICodePack-Shell -Version 1.1.1

first of all you should know that this cool solution needs you to install related program on the server, for instance if you want the shell to generate thumbnail for PDF files, you should install a PDF reader like Acrobat Reader or Foxit PhantomPDF or some thing like them on the server, it means server will create thumbnail for files which it recognizes them, and it makes sense.

Secondly, check to know which file extensions are generated thumbnail for, in the other words, check whether .psd or .msi file extensions have proper thumbnail or not, then prevent requesting server for generating thumbnail for them(check on both client end and server end).

Thirdly, you might need to get thumbnail through Ajax, personally I suggest you to give files some default thumbnails based on the file type at the first second, then request server for generating thumbnail, in that case you can use following code snippet (I receive the generated bitmap in Base64 format as image which is string actually):

Server side code:

[WebMethod]
public static string GetThumbnail(string path) {


string thumb = string.Empty;


path = @"D:\\" + path.Replace("/", "\\"); //Or Server.MapPath("/UploadedFiles");
if (File.Exists(path))
{
try
{
Microsoft.WindowsAPICodePack.Shell.ShellFile shellFile = Microsoft.WindowsAPICodePack.Shell.ShellFile.FromFilePath(path);
System.Drawing.Bitmap shellThumb = shellFile.Thumbnail.ExtraLargeBitmap;
MemoryStream ms = new MemoryStream();
shellThumb.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);//Jpeg is preferred, Png would make a bigger file size
thumb = Convert.ToBase64String(ms.ToArray());
}
catch(Exception ex)
{


}
}
return thumb;
}

Client side code:

    var url = "Default.aspx/GetThumbnail",
path = "Images/1.jpg",//For instance
extension = path.split(".").pop().toLowerCase(),
allowedExtensions = ["jpg", "jpeg", "png", "gif", "pdf", "mp4"];
    

if (allowedExtensions.includes(extension)){
$.ajax({
type: 'POST',
contentType: "application/json; charset=utf-8",
url: url,
data: "{'path':'" + path + "'}",
async: true,
xhrFields: {
withCredentials: true
},
success: function (response) {
if (!$.isEmptyObject(response.d))
$(elem).find("img").attr("src", "data:image/jpg;base64," + response.d);
},
error: function (err) {
console.error(err);
}
});
}

Take into consideration that since returned string might be a long text, you may run into an error saying:

Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property base64

in that case you have to add following code in web.config file:

  <system.web.extensions>
<scripting>
<webServices>
<jsonSerialization maxJsonLength="2147483647"/>
</webServices>
</scripting>
</system.web.extensions>

maxJsonLength is an integer value and can be Int32.MaxValue, you can read more here.