Force Read-only open

I know there has been a lot of discussion already on this topic, but is there a way to force a drawing to be opened in read-only mode in SDI?

Previous posts have supplied the code:
(defun openRO (fna)
(vla-activate (vla-open (vla-get-documents (vlax-get-acad-object)) fna :VLAX-TRUE))
)
Which is fine for MDI, but won't work in SDI.

The option I am using at the moment is to use dos_attrib to set the read-only file attribute before opening and reset it after the file is open.

If there is a more failsafe method, I would love to know.

Dean

 

I have been using something very similar to the code below, and it has been working so far. It opens (or attempts to open) the file with lisp first, and then in AutoCAD.

(setq r (open dwg "a"))
(command "._open" dwg "y")
(if (/= r nil) close r)

If the drawing is already read-only, it cannot be opened with append and "r" is set to nil. If the drawing is not initially read-only, it will be after you open it with append first.

Hope this helps. If anyone sees a problem with doing things this way, I'd be interested to hear.

Thanks.