{Following code needs to use ShlObj, ComObj, ActiveX Units}
function TForm1.IfFolderShared(FullFolderPath: string): Boolean;
 //Convert TStrRet to string
 function StrRetToString(PIDL: PItemIDList; StrRet: TStrRet; Flag: string = ''): string;
 var
  P: PChar;
 begin
  case StrRet.uType of
  STRRET_CSTR:
  SetString(Result, StrRet.cStr, lStrLen(StrRet.cStr));
  STRRET_OFFSET:
  begin
  P := @PIDL.mkid.abID[StrRet.uOffset - SizeOf(PIDL.mkid.cb)];
  SetString(Result, P, PIDL.mkid.cb - StrRet.uOffset);
  end;
  STRRET_WSTR:
  if Assigned(StrRet.pOleStr) then
  Result := StrRet.pOleStr
  else
  Result := '';
  end;
  { This is a hack bug fix to get around Windows Shell Controls returning
  spurious "?"s in date/time detail fields }
  if (Length(Result) > 1) and (Result[1] = '?') and (Result[2] in ['0'..'9']) then
  Result := StringReplace(Result, '?', '', [rfReplaceAll]);
 end;
 //Get Desktop's IShellFolder interface
 function DesktopShellFolder: IShellFolder;
 begin
  OleCheck(SHGetDesktopFolder(Result));
 end;
 //delete the first ID from IDList
 function PIDL(IDList: PItemIDList): PItemIDList;
 begin
  Result := IDList;
  Inc(PChar(Result), IDList^.mkid.cb);
 end;
 //get the length of IDList
 function GetPIDLSize(IDList: PItemIDList): Integer;
 begin
  Result := 0;
  if Assigned(IDList) then
  begin
  Result := SizeOf(IDList^.mkid.cb);
  while IDList^.mkid.cb <> 0 do
  begin
  Result := Result + IDList^.mkid.cb;
  IDList := PIDL(IDList);
  end;
  end;
 end;
 //get ID count from IDList
 function GetItemCount(IDList: PItemIDList): Integer;
 begin
  Result := 0;
  while IDList^.mkid.cb <> 0 do
  begin
  Inc(Result);
  IDList := PIDL(IDList);
  end;
 end;
 //create an ItemIDList object
 function CreatePIDL(Size: Integer): PItemIDList;
 var
  Malloc: IMalloc;
 begin
  OleCheck(SHGetMalloc(Malloc));
  Result := Malloc.Alloc(Size);
  if Assigned(Result) then
  FillChar(Result^, Size, 0);
 end;
 function CopyPIDL(IDList: PItemIDList): PItemIDList;
 var
  Size: Integer;
 begin
  Size := GetPIDLSize(IDList);
  Result := CreatePIDL(Size);
  if Assigned(Result) then
  CopyMemory(Result, IDList, Size);
 end;
 //get the last ItemID from AbsoluteID
 function RelativeFromAbsolute(AbsoluteID: PItemIDList): PItemIDList;
 begin
  Result := AbsoluteID;
  while GetItemCount(Result) > 1 do
  Result := PIDL(Result);
  Result := CopyPIDL(Result);
 end;
 //remove the last ID from IDList
 procedure StripLastID(IDList: PItemIDList);
 var
  MarkerID: PItemIDList;
 begin
  MarkerID := IDList;
  if Assigned(IDList) then
  begin
  while IDList.mkid.cb <> 0 do
  begin
  MarkerID := IDList;
  IDList := PIDL(IDList);
  end;
  MarkerID.mkid.cb := 0;
  end;
 end;
 //if Flag include Element
 function IsElement(Element, Flag: Integer): Boolean;
 begin
  Result := Element and Flag <> 0;
 end;
var
 P: Pointer;
 NumChars, Flags: LongWord;
 ID, NewPIDL, ParentPIDL: PItemIDList;
 ParentShellFolder: IShellFolder;
begin
 Result := False;
 NumChars := Length(FullFolderPath);
 P := StringToOleStr(FullFolderPath);
 //get the folder's full ItemIDList
 OleCheck(DesktopShellFolder.ParseDisplayName(0, nil, P, NumChars, NewPIDL, Flags));
 if NewPIDL <> nil then
 begin
  ParentPIDL := CopyPIDL(NewPIDL);
  StripLastID(ParentPIDL); //get the folder's parent object's ItemIDList
  ID := RelativeFromAbsolute(NewPIDL); //get the folder's relative ItemIDList
  //get the folder's parent object's IShellFolder interface
  OleCheck(DesktopShellFolder.BindToObject(ParentPIDL, nil, IID_IShellFolder,
  Pointer(ParentShellFolder)));
  if ParentShellFolder <> nil then
  begin
  Flags := SFGAO_SHARE;
  //get the folder's attributes
  OleCheck(ParentShellFolder.GetAttributesOf(1, ID, Flags));
  if IsElement(SFGAO_SHARE, Flags) then Result := True;
  end;
 end;
end;
{How to use the function?
 The parameter in is the full path of a folder}
procedure TForm1.Button1Click(Sender: TObject);
begin
 if IfFolderShared('C:\My Documents\WinPopup') then ShowMessage('shared')
 else
  ShowMessage('not shared');
end;