Question

I’m having pretty abnormal work in my application. I’m using following code to enumerate all namespaces and some root namespaces – such as Nethood work pretty slow – over one minute to load (!!) That happens only on Win7, on older system loading is OK.

I’m using this functions, from MustangPeak library:

function TNamespace.EnumerateFolder(MessageWnd: HWnd; Folders, NonFolders,
  IncludeHidden: Boolean; EnumFunc: TEnumFolderCallback;
  UserData: Pointer): integer;
var
  Enum: IEnumIDList;
  Flags: Longword;
  Fetched: Longword;
  Item: PItemIDList;
  Terminate: Boolean;
  OldError: integer;
  OldWow64: Pointer;
begin
  Result := 0;

  OldError := SetErrorMode(SEM_FAILCRITICALERRORS or SEM_NOOPENFILEERRORBOX);
  try
    if Assigned(ShellFolder) then
    begin
      if Assigned(EnumFunc) then
      begin
        Terminate := False;
        Flags := 0;
        if Folders then
          Flags := Flags or SHCONTF_FOLDERS;
        if NonFolders then
          Flags := Flags or SHCONTF_NONFOLDERS;
        if IncludeHidden then
          Flags := Flags or SHCONTF_INCLUDEHIDDEN;

    // --- This is new added
    Flags := Flags or SHCONTF_ENABLE_ASYNC;

        if Valid then
        begin
          OldWow64 := Wow64RedirectDisable;
          try

            if ShellFolder.EnumObjects(MessageWnd, Flags, Enum) = NOERROR  then
            begin
              // Vista Enum is nil every once in a while
              if Assigned(Enum) then
              begin
                while (Enum.Next(1, Item, Fetched) = NOERROR) and not Terminate do
                begin
                  if EnumFunc(MessageWnd, Item, Self, UserData, Terminate) then
                   Inc(Result)
                end
              end
            end
          finally
            Wow64RedirectRevert(OldWow64)
          end
        end
      end
    end
  finally
    SetErrorMode(OldError);
  end
end;

Now I read in MSDN doc that in Win7 new async flag has been supported in order to get results instantly but then to receive other results when system read it.

That flag is called SHCONTF_ENABLE_ASYNC and I added it in code on place I’ve marked with (// — This is new added)

Problem is because I don’t know how to catch events when I receive updates.

How to hook on newly received items? Is there some event (message etc.) that system (object) sends to some control or structure etc.

Thanks!

Answer 1

SHCONTF_ENABLE_ASYNC does not make the enumeration itself asynchronous. It simply lets IShellFolder know that you are monitoring for asynchronous change notifications outside of IShellFolder, such as with SHChangeNotifyRegister(), so the enumeration does not need to return everything at one time as the change notifications will let you know when items are added/removed/changed in real-time.