SHChangeNotify not updating URL= change in my .url shortcut file - windows

Question

I have a simple Delphi application that creates a desktop shortcut for a URL. It makes a two-line text file with a .url filename extension in the user's Desktop folder:
[InternetShortcut]
URL=http://127.0.0.1/admin
That works fine. When I need to update the file with a new URL, I overwrite the old file. But Windows will not recognize the change until I restart Explorer or reboot. So I learned about SHChangeNotify() and called it after overwriting the file:
SHChangeNotify(SHCNE_UPDATEITEM, SHCNF_PATH or SHCNF_FLUSH, PChar(Path), nil);
But it has no effect:
I tried with and without the SHCNF_FLUSH flag;
also the SHCNF_FLUSHNOWAIT flag makes no difference.
I also tried deleting the file first and then using the SHCNE_DELETE event and then re-creating the file. That doesn't work either, it just keeps using the old URL.
How do I force Explorer to reload the URL from the file without a restart?

Answer 1

While the file's content can be treated like any INI file I yet have not found a direct way to control manipulations to it:
When creating a file its content is read as expected: the system's default application for the URL='s protocol is started (i.e. for http it is most likely the internet browser).
Modifying the file per file systems has no effect - either MSIE itself maintains a cache or the COM's magic.
Indirectly manipulation is possible in the following way:
Empty the file's existing content. Why? Because the later step will just add the same INI section with an URL= value again, but the first section's URL= value remains the one that is taken into account.
Access the file per COM and change its properties. Sadly this writes more into the file - in my case the outcome/file's content was:
[{000214A0-0000-0000-C000-000000000046}]
Prop3=19,2
[InternetShortcut]
URL=http://127.0.0.1/index.php
IDList=
However, it "works" as in: the change (speak: a different URL) is recognized. Putting it all together my following code for Delphi 7 on Windows 7 should also work for you - just call the function:
uses
ShlObj, ActiveX, ComObj;
const
SID_IUniformResourceLocatorA= '{FBF23B80-E3F0-101B-8488-00AA003E56F8}';
SID_IUniformResourceLocatorW= '{CABB0DA0-DA57-11CF-9974-0020AFD79762}';
SID_InternetShortcut= '{FBF23B40-E3F0-101B-8488-00AA003E56F8}';
type
PUrlInvokeCommandInfoA= ^TUrlInvokeCommandInfoA;
TUrlInvokeCommandInfoA= record
dwcbSize,
dwFlags: DWORD; // Bit field of IURL_INVOKECOMMAND_FLAGS
hwndParent: HWND; // Parent window. Valid only if IURL_INVOKECOMMAND_FL_ALLOW_UI is set.
pcszVerb: LPCSTR; // Verb to invoke. Ignored if IURL_INVOKECOMMAND_FL_USE_DEFAULT_VERB is set.
end;
PUrlInvokeCommandInfoW= ^TUrlInvokeCommandInfoW;
TUrlInvokeCommandInfoW= record
dwcbSize,
dwFlags: DWORD;
hwndParent: HWND;
pcszVerb: LPCWSTR;
end;
IUniformResourceLocatorA= interface( IUnknown )
[SID_IUniformResourceLocatorA]
function SetURL( pcszURL: LPCSTR; dwInFlags: DWORD ): HRESULT; stdcall;
function GetURL( ppszURL: LPSTR ): HRESULT; stdcall;
function InvokeCommand( purlici: PUrlInvokeCommandInfoA ): HRESULT; stdcall;
end;
IUniformResourceLocatorW= interface( IUnknown )
[SID_IUniformResourceLocatorW]
function SetURL( pcszURL: LPCWSTR; dwInFlags: DWORD ): HRESULT; stdcall;
function GetURL( ppszURL: LPWSTR ): HRESULT; stdcall;
function InvokeCommand(purlici: PUrlInvokeCommandInfoW ): HRESULT; stdcall;
end;
function SetURL( sFile, sUrl: Widestring ): Integer;
const
CLSID_InternetShortCut: TGUID= SID_InternetShortcut;
var
oUrl: IUniformResourceLocatorW;
oFile: IPersistFile;
hFile: THandle;
begin
// First, the existing file's content should be emptied
hFile:= CreateFileW( PWideChar(sFile), GENERIC_WRITE, 0, nil, OPEN_EXISTING, 0, 0 );
if hFile= INVALID_HANDLE_VALUE then begin
result:= 1; // File might not exist, sharing violation, etc.
exit;
end;
// Initial file pointer is at position 0
if not SetEndOfFile( hFile ) then begin
result:= 2; // Missing permissions, etc.
CloseHandle( hFile );
exit;
end;
// Gracefully end accessing the file
if not CloseHandle( hFile ) then begin
result:= 3; // File system crashed, etc.
exit;
end;
// Using COM to access properties
result:= 0;
try
oUrl:= CreateComObject( CLSID_InternetShortCut ) as IUniformResourceLocatorW;
except
result:= 4; // CLSID unsupported, COM not available, etc.
end;
if result<> 0 then exit;
// Opening the file again
oFile:= oUrl as IPersistFile;
if oFile.Load( PWideChar(sFile), STGM_READWRITE )<> S_OK then begin
result:= 5; // Sharing violations, access permissions, etc.
exit;
end;
// Set the property as per interface - only saving the file is not enough
if oUrl.SetURL( PWideChar(sUrl), 0 )<> S_OK then begin
result:= 6;
exit;
end;
// Storing the file's new content - setting only the property is not enough
if oFile.Save( PWideChar(sFile), TRUE )<> S_OK then begin
result:= 7;
exit;
end;
// Success!
result:= 0;
end;
As per my desktop firewall the executing process modifies the memory of explorer.exe upon IPersistFile.Save() - after that executing the URL file should reflect its new content, while any attempt before that should still act upon the old file's content.