Help - Understanding ATTRIBUTED BLOCK definitions...

[lamensterms]

Hey guys,

Ive been having an interesting little issue trying to update some BLOCK definitions in our shop drawings.

There are 2 kinds of BLOCKs that need to be updated, 1 regular BLOCK and 1 ATTRIBUTED BLOCK.

Now... to set the scene, I have to erase and existing block and redefine, so the new block can be inserted at a later date... sort of.

The regular block I had no issue with. I have been using a variety of REFEDIT and ERASE>PURGE>PASTECLIP to redefine this block (which suited the scenario).

I have been having a little difficulty with the ATTRIBUTED BLOCK. No matter what I had done in terms of redefining - I could not get the existing blocks (of the same definition) or any newly inserted blocks to reflect my new definition.

Until I found this thread....http://forums.autodesk.com/t5/AutoCA...t/td-p/2949736

...which suggested i use the ATTSYNC command after REDEFINE. After a little mucking around, I have managed to get the ATTRIBUTED BLOCKS (present and future) to reflect the new definition.

So... I'm just wondering if someone can please explain why we have to use ATTSYNC to force ATTRIBUTED BLOCKS to update to the latest definition of the block.

PS: The new definition of this ATTRIBUTED BLOCK involved simply moving 1 of the attributes within the block.

Thanks for any help.

[ReMark]

ATTSYNC
"Use this command to update all instances of a block containing attributes that were redefined using the BLOCK or BEDIT commands. ATTSYNC does not change any values assigned to attributes in existing blocks."

[lamensterms]

Thanks for the reply ReMark.

I was really just wondering if anyone could explain why ATTRIBUTE locations are not automatically updated when a BLOCK is redefined.

Cheers.

[danellis]

Because one of the advantages that attributes in blocksa have over text in blocks is that their position can be changed, so AutoCAD needs the ATTSYNC command so that it knows that you want to change the attribute's, well, attributesto reflect the block definition, rather than the custom settings you've already given it (even if those "custom" settings are just the defaults from the previous block definition).

dJE

[lamensterms]

I see. So will ATTSYNC force these ATTRIBUTE locations to reflect the manually set locations (as per the most recent block definition) and override the ATTRIBUTES defined location?

Thanks for the reply danellis.

[irneb]

No, AttSync actually does it the other way round. Usually it's possible to grip edit an attribute of a placed block (e.g. move/scale/rotate only that one instance). Or you can also edit the properties of an attribute inside the EAttEdit dialog (or even using the properties palette while picking attributes using Ctrl for nested entities).

So when you AttSync it removes such edits and reverts all the instances of the block to reflect exactly what's inside the block definition. If you've redefined the definition, then the new definition will be applied to all references of that block only by the AttSync command.

If you want to know more fully what's really happening with attributes, read on:

If a block has AttDef entities inside it, all insertions of that block may have linked Attrib entities following them. These Attrib entities are separate from the block, but ACad sees that they should work as if they're part of it. You may adjust individual Attrib entities to different positions or properties as their corresponding AttDef entity (inside the block definition) had.

When you redefine / BEdit / RefEdit such block, any changes to the AttDef entities won't automatically be reflected on the existing Insertions of that block. This is done so that the individual edits (if any) won't simply be undone every time a block is redefined. For such purpose the AttSync command (or its bigger brother the BAttMan command - Block Attribute Manager, not the super-hero ) is available to update the attributes if you want it thus.

There are a few serious problems with the AttSync/BAttMan commands though:

1. They are both an all or nothing command. I.e. they will update all attributes in all insertions of the block, and all the positions / properties will be updated to match the AttDefs inside the block. To avoid this cut the doors (??? ... uhm no ...) edited blocks out of the DWG, perform the AttSync and the paste them back to original coordinates - unfortunately they won't be updated at all then. For more fine-grained you'd need some lisp or so.
2. If you have a block which is mirrored, the attributes will also become mirrored - no matter what your MirrText is set to. To avoid, first mirror the mirrored blocks then perform AttSync & then mirror them back.
3. If you rename an AttDef all old references of it will be deleted and recreated with the default values. To avoid use BAttMan to rename attributes.

[lamensterms]

Ahah... i think i understand now - and it does coincide with what I have been experiencing while updating my blocks.

Thanks so much for taking the time to explain irneb. Im just beginning to scratch the surface with special BLOCK and ATTRIBUTE behavior and I really appreciate the advice.

Cheers.