How to remove objects from a drawing

Samuel_A

I have several objects on a DWG drawing that I want to delete when I load the drawing. It is a single block that is in one specific layer and used all over the drawing.
So what I want is some way to check if an object on screen is this specific one and remove it. I couldn't find any examples for this. I only found one example that loops through all objects on screen and I was able to detect the ones I want to remove, but how to remove them? I tried several things but nothing worked.

This is the program code I tried:

void deleteObjects()
{
AcDbBlockReference* pBlockRef;
AcDbDatabase* pDb = acdbHostApplicationServices()->workingDatabase();

// Get the current space object
AcDbBlockTableRecord* pBlockTableRecord;
Acad::ErrorStatus es = acdbOpenObject(pBlockTableRecord, pDb->currentSpaceId(), AcDb::kForRead);

// Create a new block iterator that will be used to step through each object in the current space
AcDbBlockTableRecordIterator* pItr;
pBlockTableRecord->newIterator(pItr);

// Create a variable AcDbEntity type which is a generic object to represent a Line, Circle, Arc, among other objects
AcDbEntity* pEnt;

// Step through each object in the current space
for (pItr->start(); !pItr->done(); pItr->step())
{
// Get the entity and open it for read

pItr->getEntity(pEnt, AcDb::kForRead); // I tried to put kForWrite here instead but that crashed the program instead

TCHAR* layerName = pEnt->layer();

// Check if entity is on the layer we want
if (_tcscmp(layerName, LAYERSTR_OFFSET) == 0)
{
// This works so that when I am here it is for one of the objects I want to remove

pEnt->erase(); // This doesn't work so it wasn't that easy
/*
// I tried the following code to see if that helped but no result
pBlockRef = AcDbBlockReference::cast(pEnt);
bool bBlockFound = (pBlockRef != NULL);

if (bBlockFound)
{
pBlockRef->erase();
}*/
}
pEnt->close();
}

// Close the current space object
pBlockTableRecord->close();

// Remove the block iterator object from memory
delete pItr;
}

Jason Bourhill

If you're open to LISP, then this is an easy thing to do.

(ssget "X" '((0 . "INSERT")(2 . "BLOCK_NAME")(8 . "BLOCK_LAYER")))

Will create a selection set of all the blocks called "BLOCK_NAME" on the the drawing that are on the layer "BLOCK_LAYER".

You can use this to build a function to delete the blocks

(defun DeleteBlocks ( / sset odoc ent num) 
	(setq sset (ssget "X" '((0 . "INSERT")(2 . "BLOCK_NAME")(8 . "BLOCK_LAYER"))))
	(cond 
		(sset
			(princ (strcat "\nFound " (itoa (sslength sset)) " Blocks to delete"))
			(setq odoc (vla-get-activedocument (vlax-get-acad-object))) ; retrieve active document
			(vla-endundomark odoc)
			(vla-startundomark odoc) ; set undo mark
			(setq num 0)
			(foreach ent (vle-selectionset->list sset)
				(if (entdel ent) (setq num (1+ num)))
			)
			(vla-endundomark odoc)
			(princ (strcat "\nDeleted " (itoa num) " Blocks\n"))
		)
		(T (Princ "\nBlock not found.\n"))
	)
	num
)

You add a call to this function in your on_doc_load.lsp to run automatically each time a drawing file is opened.

Regards,
Jason Bourhill
BricsCAD V22 Ultimate
CAD Concepts

Joe Dunfee

The purge command would permit you to select a specific block. Below would be the sequence of commands to use, with what I type in bold capitals. This example would purge all blocks named "door".

PURGE
Purge: BAtch/All/Blocks/Dimstyles/LAyers/LTypes/MAterials/MLinestyles/Plotstyles/STyles/Tablestyles/Visualstyles/Regapps: BLOCK
Enter name(s) to purge <*>: DOOR <-TYPE THE NAME OF THE BLOCK</i>
Verify each name to be purged? [Yes/No] : N
:
So, you could create a macro that you could manually run. Or if you wanted it to run automatically, then either save as a script, that you run from the startup lisp. Or even just use the command feature of LISP to send those commands.

-Joe

Samuel_A

I have never done anything with LISP, but this code needs to be inside the C++ application so it must be in C++ code. I just want to remove all objects of a specific block from the drawing and it must be some way to do it?

Joe Dunfee

While sending keystrokes is not generally the best way to do things, just sending the keystrokes as though you were typing at a keyboard is one way to do it. Though I don't know if there is a way to get the program to run when a drawing opens, other than putting a command to load the C program inside the startup lisp file.

-Joe

Samuel_A

I found some examples using the acedSSGet function and that worked better. The following code almost works. It works first time I tries it, but if I open a new drawing it gives error "corrupt drawing, error in database" and with the debugger I can see that it is the acedSSGet command that crash, but why?

ads_name pName;
struct resbuf eb;
TCHAR sbuf[100];

eb.restype = 8; // Layer name filter
_tcscpy(sbuf, LAYERSTR_OFFSET);
eb.resval.rstring = sbuf;
eb.rbnext = NULL;
acedSSGet(_T("X"), NULL, NULL, &eb, pName); // Retrieve all entities on layer

long number = 0;
if ((acedSSLength(pName, &number) != RTNORM) || (number == 0))
{
acedSSFree(pName);
}
ads_name ent;
AcDbObjectId id = AcDbObjectId::kNull;

// Open to delete
for (long i = 0; i < number; i++)
{
acedSSName(pName, i, ent) != RTNORM;
acdbGetObjectId(id, ent);
AcDbEntity* pEnt = NULL;
acdbOpenAcDbEntity(pEnt, id, AcDb::kForWrite);
pEnt->erase();
pEnt->close();
}
acedSSFree(pName);

Samuel_A

I removed everything so only this code is active and is triggered after a dwg file is loaded

ads_name pName = { 0,0 };
acedSSGet(NULL, NULL, NULL, NULL, pName);
acedSSFree(pName);

It still gives error. First time I load a drawing it works, but when I close the drawing and open it again (or another) it gives error that file is corrupt and database error.

Samuel_A

I got the first version working. I just had to change the entity from read to write with "pEnt->upgradeOpen();" command and after that I could do erase on it, but why the second example isn't working is another thing.