Update Image Thumbnail from c#

Question

I am manipulating JPEG images programmatically from C# in a WinForms app in Win 10 and would like File Explorer to show the manipulated rather than the original image thumbnail. Closing Explorer, deleting %LocalAppData%\Microsoft\Windows\Explorer\thumbcache_*.db and restarting does this but it is slow and intrusive. I would like to update an individual file's thumbnail programmatically. Windows does this when an image is rotated via the Explorer context menu, but the means for doing this from a program aren't clear.

The batch file which I currently use to close Explorer, delete the thumbnail cache file and restart is

taskkill /f /im explorer.exe
timeout 2 /nobreak>nul
DEL /F /S /Q /A %LocalAppData%\Microsoft\Windows\Explorer\thumbcache_*.db
timeout 2 /nobreak>nul
start "" %windir%\explorer.exe
start "" %windir%\explorer.exe "Folder To Update"

Nothing useful that I can run programmatically. Explorer Rotate option changes thumbnail though. — SimonKravis, Apr 14 '20 at 04:54
Tried method described in https://stackoverflow.com/questions/3555799/how-do-i-refresh-a-files-thumbnail-in-windows-explorer in 2010, but does not work in Win 10. — SimonKravis, Apr 14 '20 at 08:26

Dmitry Brant · Answer 1 · 2020-04-15T14:15:43.270

0

The proper way to do something like this is to use the SHChangeNotify() function. If you're using C#, you can p/invoke it like so:

[DllImport( "Shell32.dll", CharSet = CharSet.Auto, SetLastError = true )]
static extern void SHChangeNotify(uint wEventId, uint uFlags, [MarshalAs(UnmanagedType.LPWStr)] string dwItem1, IntPtr dwItem2);

...and then use it to notify Explorer that an item has been modified (i.e. the image that you manipulated):

private const uint SHCNE_UPDATEITEM = 0x00002000;
private const uint SHCNF_PATHW = 0x0005;
private const uint SHCNF_FLUSH = 0x1000;

string pathName = "your image file.jpg"

SHChangeNotify(SHCNE_UPDATEITEM, SHCNF_PATHW | SHCNF_FLUSH, pathName, IntPtr.Zero);

edited Apr 15 '20 at 14:15

answered Apr 15 '20 at 13:08

Dmitry Brant

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You can declare SHChangeNotify with item1 (and/or item2) like this to avoid allocations: `[MarshalAs(UnmanagedType.LPWStr)] string dwItem1` – Simon Mourier Apr 15 '20 at 13:54
Tried this suggestion with the change that 3rd argument of SHChangeNotify is an integer pointer rather than a string as follows `intPtr pidl; SHParseDisplayName(path, IntPtr.Zero, out pidl, 0, out iAttribute); SHChangeNotify( SHCNE_UPDATEITEM, SHCNF_FLUSH|SHCNF_PATHW, pidl, IntPtr.Zero);` but still does not change thumbnail in Explorer on Win 10. – SimonKravis Apr 16 '20 at 02:02
The integer pointer was needed due to a different declaration of SHChangeNotify as follows `internal static extern void SHChangeNotify( UInt32 wEventId, UInt32 uFlags, IntPtr dwItem1, IntPtr dwItem2`. Changing to one supplied by Dmitry Brant and passing path as string did not change thumbnail either. – SimonKravis Apr 16 '20 at 03:59
Research indicates that calls to SHChangeNotify from outside the shell may not work. This may explain observations. – SimonKravis Apr 17 '20 at 02:00

score -2 · Accepted Answer · answered Apr 16 '20 at 06:18

Increasing the file modified date by 1 sec and then changing it back triggers Windows into thinking the file has changed so that the thumbnail is updated. Code used is

DateTime modDate = System.IO.File.GetLastWriteTime(sFile);
System.IO.File.SetLastWriteTime(sFile, modDate.AddSeconds(1.0));
System.IO.File.SetLastWriteTime(sFile, modDate.AddSeconds(-1.0));

Update Image Thumbnail from c#

2 Answers2