Topic: Entity Handles

[QuestionEverything]

What are entity handles, and more importantly what are they used for?

[Lee Mac]

Welcome to The Swamp.

I assume you have already read the existing developer documentation?

http://help.autodesk.com/view/ACD/2015/ENU/?guid=GUID-30C33AF6-4BE3-4334-96BD-F929040C31D3

[QuestionEverything]

Hello, thanks for welcoming me.
 I have been reading about them several times but still can't seem to find any practical usage.. so what are they used for?

[MP]

Handles provide the means to perform a wide spectrum of activities including inter object linking, serialization, database use etc. tl;dr: they're invaluable. Welcome to the best AutoCAD website on the web.

[QuestionEverything]

Hi,
As far I can understand, using "handles" I would be able to store a list of entities, end the drawing session, then in a new session I could access that same entities and for example erase them or grip them in a selection set. Is that correct ? Do you have any practical explanations or examples?

[dgorsman]

Handles provide the means to perform a wide spectrum of activities including inter object linking, serialization, database use etc. tl;dr: they're invaluable. Welcome to the best AutoCAD website on the web.

Well, that's what they can be used for.  What they are, is a unique index in the drawing database.  Each handle will refer to one and only one object (not all entities are objects, but all objects have a handle); each object will have one, and only one, handle.  The handle doesn't change, either in the drawing session or between drawing sessions (it may appear to do so in some circumstances, however what is happening is the original object is being copied or recreated - hence the new handle).  Handles are NOT unique between drawings.

One of our third-party programs provides the option to manage part data in an associated database.  It uses a combination of DWG filename and handle to uniquely identify which part in the database is which part in the DWG file.

[MP]

Ummm. Lee already addressed the "what are handles?" question, I responded to the "what are they used for?" question.

[QuestionEverything]

Ummm. Lee already addressed the "what are handles?" question, I responded to the "what are they used for?" question.

Okay, I understood "what are handles", but still can't seem to understand their usage. Any simple and precise examples?

(setq ent (car (entsel)))
(setq data (entget ent))
(setq hand (cdr (assoc 5 data)))
(setq handy (handent hand))

What can I do with 'handy' or 'hand' once I have them?

[ribarm]

Ummm. Lee already addressed the "what are handles?" question, I responded to the "what are they used for?" question.

Okay, I understood "what are handles", but still can't seem to understand their usage. Any simple and precise examples?

(setq ent (car (entsel)))
(setq data (entget ent))
(setq hand (cdr (assoc 5 data)))
(setq handy (handent hand))

What can I do with 'handy' or 'hand' once I have them?

You can store them inside variables after you can save them into *.txt file and reuse them in next CAD session - here is this one example :
http://forums.autodesk.com/t5/visual-lisp-autolisp-and-general/extract-a-text-from-a-long-text/m-p/5955380/highlight/true#M337556

To save variables during session in some *.txt file, check another link from post that I just pointed out...

So that's one example of using handles... I must admit I don't use them a lot, but someone else may show something else also interesting...

M.R.

[danallen]

An example might be to remember a specific entity, though that could be done with selection set. I have a couple examples in my code library

Code - Auto/Visual Lisp: [Select]

1. ;;;  by sinc @ the Swamp  07/22/2004
2. ;;;  Repeatedly draws a line from a pick point perpendicular
3. ;;;  to a selected object
4. ;;;  modified by Dan Allen to remember entity between uses
5. (defun c:lp (/ entity pt deleted)
6.   (princ "\nDraw perpedicular lines from selected entity")
7.   (if SAA_C:LP_ENTITY
8.     (progn
9.       (setq entity (car (entsel "\nSelect entity or <use last chosen>: ")))
10.       (if (and (not entity)                                             ;if nothing chosen
11.                (setq entity (handent SAA_C:LP_ENTITY))                  ;and entity can be found
12.                (setq deleted (entget (handent SAA_C:LP_ENTITY))))       ;and not deleted (entget returns nil if deleted)
13.         (princ "\nUsing last entity chosen.")
14.         (progn
15.           (if deleted
16.             (progn
17.               (setq entity nil)                         ;in case was deleted
18.               (princ "\nLast entity chosen can't be found, pick again.")
19.             ) ;_progn
20.           ) ;_if
21.         )
22.       ) ;_if
23.     ) ;_progn
24.   ) ;_if
25.   (if (not entity) (setq entity (car (entsel "\nSelect entity: "))))
26.   (if entity
27.     (progn
28.       (setq SAA_C:LP_ENTITY (cdr (assoc 5 (entget entity))))    ;remember for reuse
29.       (while
30.         (setq pt (getpoint "\nSelect point to draw perpendicular from: "))
31.          (entmake (list '(0 . "LINE") (cons 10 (trans pt 1 0))
32.             (cons 11 (vlax-curve-getClosestPointTo entity (trans pt 1 0)))) ;_ list
33.          ) ;_ entmake
34.       ) ;_ while
35.     ) ;_progn
36.   ) ;_if
37.   (princ)
38. ) ;_ defun
39.  
40. ;;;=========================================================================
41. ;;; Return previous entity in order of creation
42. ;;; entprev  -  Lee Mac 2013-11-22
43. ;;;=========================================================================
44. (defun entprev ( e1 / e2 h1 h2 )
45.     (setq h1 (cdr (assoc 5 (entget (entnext))))
46.           h2 (cdr (assoc 5 (entget e1)))
47.     )
48.     (if (/= h1 h2)
49.         (while
50.             (not
51.                 (or (= h1 (setq h2 (hex-- h2)))
52.                     (and (setq e2 (handent h2)) (entnext e2))
53.                 )
54.             )
55.             (setq e2 nil)
56.         )
57.     )
58.     e2
59. )
60.  

[QuestionEverything]

Okay guys, now theres finally a place where someone like me would understand them well enough - THIS THREAD.
Thank you all for the help!