Can't update Title Block attributes via .NET API

[bleite6S4UE]

Hi everyone!

I have a dwg file that contains a Viewport, a MTEXT and a Title Block and I'm trying to update the Title Block's attribute through the .NET API. According to AutoCAD Electrical the Title Block is of type Block Reference, but when I try to update via .NET API, it never finds it as a Block Reference, it finds it as a Block Table Record, and when I iterate through the Block  Table Record, it only finds AttributeDefinition objects, not AttributeReference objects. 

As I was reading about it, AttributeDefinition only modifies the default value for future insertions, not for current instances. To update the value of an attribute of an existing block reference I need to use AttributeReference. I can modify its AttributeDefinition objects, like change the tag, prompt or TextString, but I can't modify the existing instance of the Title Block. 

When I run the .NET application, it finds all 4 blocks, 2 are block references, the other 2 aren't. 

This is the piece of code that is trying to find and modify the title block:

Database db = new Database(false, true);
db.ReadDwgFile(inputFilePath, System.IO.FileShare.Read, true, "");

// Start a transaction
using (Transaction tr = db.TransactionManager.StartTransaction())
{
    try
    {
        Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;
        // Get the block table
        BlockTable blockTable = (BlockTable)tr.GetObject(db.BlockTableId, OpenMode.ForRead);
        ed.WriteMessage($"\nBlock Table Type: {blockTable.GetType()}");

        // Iterate through each block table record
        foreach (ObjectId btrId in blockTable)
        {
            BlockTableRecord btr = (BlockTableRecord)tr.GetObject(btrId, OpenMode.ForRead);

            // Print the block name
            ed.WriteMessage($"\nBlock Record Name: {btr.Name}");
            ed.WriteMessage($"\nBlock Record Type: {btr.GetType()}");

            // Iterate through title block and modify desired lines
            foreach (ObjectId entId in btr)
            {
                Entity ent = (Entity)tr.GetObject(entId, OpenMode.ForRead);

                if (ent is BlockReference)
                {
                    ed.WriteMessage($"{ent.GetType()} is a Block Reference.");
                }

                if (ent is MText)
                {
                    MText? mtext = tr.GetObject(entId, OpenMode.ForWrite) as MText;
                }

                if (ent is AttributeDefinition)
                {
                    ed.WriteMessage($"\nEntity type: {ent.GetType()}");
                    AttributeDefinition attributeDefinition = tr.GetObject(entId, OpenMode.ForWrite) as AttributeDefinition;
                    if (attributeDefinition != null && attributeDefinition.Tag == "LOCATION")
                    {
                        ed.WriteMessage($"\nAttribution Tag: {attributeDefinition.Tag}");
                        attributeDefinition.TextString = "Kansas City";
                    }
                }
            }
        }

        // Commit the transaction
        tr.Commit();
    }
    catch (Autodesk.AutoCAD.Runtime.Exception ex)
    {
        // Handle exceptions
        Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;
        ed.WriteMessage($"Error: {ex.Message}\n");
    }
    finally
    {
        tr.Dispose();
    }
}

Any help would be much appreciate it! Thank you!!!

[Ed__Jobe · Accepted solution]

Your code is searching for block definitions, not block references (aka "INSERT"). Plus, you're working with modelspace and I would hope that your title block is in paperspace. This thread shows you how to iterate a paperspace layout's block contents and find a block by name.

[bleite6S4UE]

Thanks Ed. After a lot of try and error and some code restructuring based on what you said, I was able to find the Title Block and it did find it as a Block Reference.