Implementing IFileIsInUse - winapi

Question

I'm trying to implement the IFileIsUse COM interface in my Delphi program so that Windows Explorer can show more details about my application when it locks a file.
I based my code on the FileIsUse sample from Microsoft (http://msdn.microsoft.com/en-us/library/ee330722%28VS.85%29.aspx) and am up to this:
type
TFileIsInUseImpl = class(TInterfacedObject, IUnknown, IFileIsInUse)
protected
function GetAppName(out ppszName: LPWSTR) : HRESULT; stdcall;
function GetUsage(out pfut : FILE_USAGE_TYPE) : HRESULT; stdcall;
function GetCapabilities(out pdwCapFlags : DWORD) : HRESULT; stdcall;
function GetSwitchToHWND(out phwnd : HWND) : HRESULT; stdcall;
function CloseFile() : HRESULT; stdcall;
public
constructor Create(const AFileName: string);
end;
procedure RegisterFileIsInUse(const AFileName: string);
var
Cookie: Longint;
rot: IRunningObjectTable;
hr: HRESULT;
mk: IMoniker;
FileIsInUse: IFileIsInUse;
begin
hr := GetRunningObjectTable(0, rot);
if SUCCEEDED(hr) then
begin
hr := CreateFileMoniker(PChar(AFileName), mk);
if SUCCEEDED(hr) then
begin
FileIsInUse := TFileIsInUseImpl.Create(AFileName);
hr := rot.Register(ROTFLAGS_REGISTRATIONKEEPSALIVE or ROTFLAGS_ALLOWANYCLIENT, FileIsInUse, mk, Cookie);
if hr = CO_E_WRONG_SERVER_IDENTITY then
hr := rot.Register(ROTFLAGS_REGISTRATIONKEEPSALIVE, FileIsInUse, mk, Cookie);
if SUCCEEDED(hr) then
FRegisteredFiles.Add(AFileName, TRegisteredFile.Create(Cookie, FileIsInUse));
end;
end;
end;
I added registry infos in both HKEY_CLASSES_ROOT\AppID\MyApp.exe and HKEY_CLASSES_ROOT\AppID\{MyGUID} to indicate RunAs=Interactive user so that the first call to rot.Register succeeds with ROTFLAGS_ALLOWANYCLIENT
However, none of my TFileIsInUseImpl methods are ever called.
Overriding QueryInterface for it, I discovered that it does get called but only for marshaling related interfaces, never for IFileIsInUse.
Looking around I came to the conclusion that something is not initialized the way it should be in my application, but I can't figure out why.
I already tried this:
Call CoInitializeEx(nil, COINIT_MULTITHREADED) instead of the default CoInitialize(nil)
Add HKEY_CLASSES_ROOT\CLSID\{MyGuid}\InProcServer32\ThreadingModel=Both
but nothing helped. Considering that Microsoft's sample is a standalone application, I should be able to replicate what it does.
Can any of you tell me what I'm doing wrong here?

Answer 1

If the code was build similar to the MSDN example, then it works as expected. The sample code can be downloaded from the code gallery:
Defect link: http://archive.msdn.microsoft.com/Project/Download/FileDownload.aspx?ProjectName=shellapplication&DownloadId=6773
New link: https://msdn.microsoft.com/en-us/library/windows/desktop/ee330722(v=vs.85).aspx
Download from Windows 7 SDK: https://www.microsoft.com/en-us/download/details.aspx?id=8279