How to get the position of an nested block that changes size due to constraint parameter

[YYCad·Lover]

Hi. Thank you so much guys, for your help! this problem is bothering me.

Problem Description:
    1. I have a block "door" like a rectangle that has been shaped with automatic constraints;
    2. Then a vertical constraint parameter is built in the "Door" block: "Height", so the height is 500;
    3. In addition, an nested block like a cross is inserted: "coordinateBlock";
    4. Create a coincidence constraint on the top of the "Height" edge of "coordinateBlock" and "Door", such that the position is (0, 500);
    5. Insert the "Door" block reference in the new file through the C# API code, and modify the "Door" constraint parameter "Height" to change the block reference height, such as from 500 to 800;
    6. At this time, the position of the "coordinateBlock" has changed, and it has actually followed (0, 800);

Phenomenon:
    1. The display position of the nested block "coordinateBlock" in the "Door" block in model space has indeed become (0, 800);
    2. I have tried many methods, but I can't get the coordinate position (0, 800) after the "coordinateBlock" changes, but can only get the insert position (0, 500);

Question:
    1. Is there any way to get the position data of the inline block changed by constraints without explode the "Door" block;

Code I use:

Document acDoc = Application.DocumentManager.MdiActiveDocument;
Database acCurDb = acDoc.Database;
Editor ed = acDoc.Editor;
using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
{
    BlockTable acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId, OpenMode.ForRead) as BlockTable;
    BlockTableRecord acBlkTblRec = acTrans.GetObject(acBlkTbl[BlockTableRecord.ModelSpace], OpenMode.ForRead) as BlockTableRecord;
    
    foreach (ObjectId acObjId in acBlkTblRec)
    {
        if (acObjId.ObjectClass.Name == "AcDbBlockReference")
        {
            BlockReference bf = acObjId.GetObject(OpenMode.ForRead) as BlockReference;
            string bname = (bf.IsDynamicBlock) ? (bf.DynamicBlockTableRecord.GetObject(OpenMode.ForRead) as BlockTableRecord).Name : bf.Name;
            
            if (bname.StartsWith("Door"))
            {
                if (bf.IsDynamicBlock)
                {
                    BlockTableRecord btr = bf.DynamicBlockTableRecord.GetObject(OpenMode.ForRead) as BlockTableRecord;
                    foreach (ObjectId item in btr)
                    {
                        if (item.ObjectClass.Name == "AcDbBlockReference")
                        {
                            BlockReference btf = item.GetObject(OpenMode.ForWrite) as BlockReference;
                            string tname = (btf.IsDynamicBlock) ? (btf.DynamicBlockTableRecord.GetObject(OpenMode.ForRead) as BlockTableRecord).Name : btf.Name;

                            if (tname.StartsWith("coordinateBlock"))
                            {
                                btf.Position; // here is not change (0, 200);
                            }
                        }
                    }
                }
            }
        }
    }
    acTrans.Commit();
}

[tbrammer · Accepted solution]

When you create a dynamic BREF with a defined parameter set, the BREF doesn't point to the original block but to an unnamed block.

I used the tool ArxDbg.arx from  <ARX>\\samples\database\ARXDBG to analyse TestBlock.dwg. 
Call SNOOPENTS and select the 800mm BREF shows this:

So you see the "real" block name is "*U7".

With SNOOPDB you can examine the block *U7:

Expand the Block Table, select *U7 from the list and hit [Entities in Block].

There you find the BREF to "coordinateBlock" at position (0,800,0).

Unfortunately I can't tell you how to code this in C# - I'm more into C++.

But I think you can figure out how to do it.  

In C++ I would query the objectid of the BREF's blocktablerecord, open it and search for the nested BREF to "coordinateBlock" using an iterator.

[YYCad·Lover]

Thank you very much!

You gave me very important clues;

Since I am not very familiar with the mechanism of CAD internal block generation, it creates a new anonymous block for static blocks to show, I used the wrong way to get dynamic blocks to get static blocks;

And thank you for teaching me to use ArxDbg to view the internal relationship of graphics, this is very useful;

Finally, to share the API I found in C# to help others:

In C#, use `GetBlockReferenceIds` API to get all reference IDs of a static block, which I think are the created anonymous block IDs;

Code like:

BlockTable bt = (BlockTable)trans.GetObject(db.BlockTableId, OpenMode.ForRead);
BlockTableRecord btr = (BlockTableRecord)trans.GetObject(bt[blockName], OpenMode.ForRead);
ObjectIdCollection blockIds = btr.GetBlockReferenceIds(true, true);
foreach (ObjectId id in blockIds)
{
    BlockReference block = (BlockReference)trans.GetObject(id, OpenMode.ForRead);
    // here can get block's position
}