Undo group

[svucic]

Hello,

I'm trying to figure out the undo command in autolisp. I can't find any good documentation with examples although there are many posts on forums.

I cant get my head around Begin and Back. As far as I understood it does the same. But I can't make (command-s "._UNDO" "BE" )  to work in my code.

(command-s "._UNDO" "B" ) works fine.

Here is my code.

(defun C:InsertAtrLin ()

*
*
*
*

(defun C:VPTFL(/ *error*)

(defun *error*(errmsg)
	(if (not (wcmatch errmsg "Function cancelled,quit / exit abort,console break"))
      (princ (strcat "\nError: " errmsg))
	  
	)
	(command-s "._UNDO" "B" )
	(vl-bt)
)

	(setq *acad* (vlax-get-acad-object))
	(setq Doc (vla-get-ActiveDocument *acad*))
	(vla-startundomark Doc)

;(command "._UNDO" "_Begin" )
;(command-s "._UNDO" "_End")
(if (= rb 0)
	(progn
		(prompt "\nNacrtajte liniju!")
		(command "._PLINE")
		(while (eq 1 (logand 1 (getvar "CMDACTIVE")))
			(command pause)
		)
		(setq selline (entlast))
		(setq ssline (ssadd))   
		(ssadd selline ssline)
		
		(C:choosecodeFL)
		
		(_lindata)
		
		(_lstyle)
		
		(C:InsertAtrLin)
		
		(C:appendatrfullline)
	)
)

(if (= 8 (logand (getvar 'undoctl) 8))
(princ "\nGroup is active!")
(princ "\nGroup is not active!")
)

(if (= rb 1)
	(progn

		(C:pickline)
		
		(C:choosecodeFL)
		
		(_lindata)
		
		(_lstyle)
		
		(C:InsertAtrLin)
		
		(C:appendatrfullline)

	)
)
;(command "._UNDO" "_End")
;(command-s "._UNDO" "_Begin")
(vla-endundomark Doc)
)

(defun C:VPTIL()

(if (= rb 0)
	(progn
		(prompt "\nNacrtajte liniju!")
		(command "._PLINE")
		(while (eq 1 (logand 1 (getvar "CMDACTIVE")))
			(command pause)

*
*
*
*

)

[Alexander.Rivilis]

---

@svucic wrote:

I cant get my head around Begin and Back. As far as I understood it does the same.

---

No. Undo Begin is start undo group, Undo End is stop undo group, but Undo Back is execute Undo to last Undo Mark (or Undo all commands if no marks).

Undo Begin is the same as:

(vla-startundomark Doc)

and Undo End is the same as: 

(vla-endundomark Doc)

[svucic]

Thank you for your kind response.

OK, so Undo Back undoes everything to the last Undo Mark.  So what is the command to undo everything to Undo Begin? Is it  (command "UNDO" "BE")?

[Alexander.Rivilis]

No. Undo Mark and Undo Begin is totally different commands. Undo Mark create mark for Undo Back command, but Undo Begin begin a group of commands to undo it as one command with Undo 1 (or U) command.

http://help.autodesk.com/view/ACD/2016/ENU/?guid=GUID-2729A466-B199-4840-B92B-4D8A38A8ADB8

[svucic]

I think I get it now.

It's confusing me that when I group some code and use command U, it doesn't undo all the changes.

Could this be due nested functions. My code strucuture is something like this.

(defun C:MainFunction()

;; Main function code here
*
*
*
*
;; Main function code here

    (defun C:SubFunction( / *error*)

        (defun *error*(errmsg)
             *
             *
             *
         (command-s "U")
         (vl-bt) 
		) *error* END

		(command "._UNDO" "_Begin" ) 
		;; SubFunction code 
		(C:SomeFunction) 
		(C:SomeFunction2) 
		(_SomeFunction3) 
		* 
		* 
		* 
		;; SubFunction code 
		(command-s "._UNDO" "_End") 
			
	) ;SubFunction END 
	
) ;MainFunction END

[Alexander.Rivilis]

Oh... I can not recommend using command method in *error* function.

What about catching errors with help of (vl-catch-all-apply) function?

[svucic]

I'll have a look at that function. Anyway, I saw a lot of posts in which people are using UNDO and *error* to undo the changes made by a routine if escape is pressed or an error occurs. I just can't make that work for me and I really would like to.

[Kent1Cooper · Accepted solution]

---

@svucic wrote:

....

It's confusing me that when I group some code and use command U, it doesn't undo all the changes.

....

....
        (defun *error*(errmsg)
             *
             *
             *
         (command-s "U")
         (vl-bt) 
		) *error* END
....

---

Since your main function includes an Undo Begin, and concludes with an Undo End if all goes well, you need to give it that Undo End in the *error* handler if anything goes wrong, before giving it the "plain" U command, which will Undo everything sandwiched between the Begin and End as one "item".  Try adding a line:

....
        (defun *error*(errmsg)
             *
             *
             *

         (command "_.undo" "_end")
         (command-s "U")
         (vl-bt)
       ) *error* END
....

[or the (vla-...) equivalent].

[svucic]

That's it! Thank you very much Kent1Cooper!