Is it possible to edit block attributes in AutoCAD using Autodesk.AutoCAD.Interop?

Question

I have developed an external WPF application to generate drawings in c#. I have been able to draw, dimension, add blocks and every thing else required by the application using Autodesk.AutoCAD.Interop, however I can't seem to populate The title block, or generate a parts list.

All the examples I've seen are based on the mechanism that requires the application to run as a plugin inside AutoCAD. The truth is, inserting a line used is one or two lines of code using ModelSpace.InsertLine, now, it's at least 8 lines of code!

Is there a way to achieve this functionality using the Autodesk.AutoCAD.Interop? Or is there a way to combine using the interop with a plugin that can be called from the external exe?

Any pointers on this will be appreciated.

Thanks.

EDIT To illustrate:

// before - Draw Line with Autodesk.AutoCAD.Interop
private static AcadLine DrawLine(double[] startPoint, double[] endPoint)
{
    AcadLine line = ThisDrawing.ModelSpace.AddLine(startPoint, endPoint);
    return line;
}
// Now - Draw line with Autodesk.AutoCAD.Runtime
[CommandMethod("DrawLine")]
public static Line DrawLine(Coordinate start, Coordinate end)
{
    // Get the current document and database 
    // Get the current document and database
    Document acDoc = Application.DocumentManager.MdiActiveDocument;
    Database acCurDb = acDoc.Database;

    // Start a transaction
    using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
    {
        // Open the Block table for read
        BlockTable acBlkTbl;
        acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId, OpenMode.ForRead) as BlockTable;

        // Open the Block table record Model space for write
        BlockTableRecord acBlkTblRec;
        acBlkTblRec = acTrans.GetObject(acBlkTbl[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord;

        // Create a line that starts at 5,5 and ends at 12,3
        Line acLine = new Line(start.Point3d, end.Point3d);

        acLine.SetDatabaseDefaults();

        // Add the new object to the block table record and the transaction
        acBlkTblRec.AppendEntity(acLine);
        acTrans.AddNewlyCreatedDBObject(acLine, true);

        // Save the new object to the database
        acTrans.Commit();
        return acLine;
    }
}

Answer 1

Yes, you can absolutely combine the two approaches.

1. Write an in-process DLL that does the work in AutoCAD. Make the commands you wish to call available to the command line by flagging your public methods with [CommandMethod("MethodName")].

2. Get AutoCAD started or connected via interop calls.

3. Using the interop AcadApplication, netload your DLL, and then call your work functions from the command line.

*Bonus * You can pass interop parameters to internal commands much easier this way too.

Here's an example of how you could build a commandmethod in-process and then call it via COM:

[CommandMethod("EditBlockAtt")]
public void EditBlockAtt()
{
    var acDb = HostApplicationServices.WorkingDatabase;
    var acEd = AcadApplication.DocumentManager.MdiActiveDocument.Editor;

    var blockNamePrompt = acEd.GetString(Environment.NewLine + "Enter block name: ");
    if (blockNamePrompt.Status != PromptStatus.OK) return;
    var blockName = blockNamePrompt.StringResult;

    var attNamePrompt = acEd.GetString(Environment.NewLine + "Enter attribute name: ");
    if (attNamePrompt.Status != PromptStatus.OK) return;
    var attName = attNamePrompt.StringResult;

    var acPo = new PromptStringOptions(Environment.NewLine + "Enter new attribute value: "){ AllowSpaces = true };
    var newValuePrompt = acEd.GetString(acPo);
    if (newValuePrompt.Status != PromptStatus.OK) return;
    var newValue = newValuePrompt.StringResult;

    using (var acTrans = acDb.TransactionManager.StartTransaction())
    {
        var acBlockTable = acTrans.GetObject(acDb.BlockTableId, OpenMode.ForRead) as BlockTable;
        if (acBlockTable == null) return;

        var acBlockTableRecord = acTrans.GetObject(acBlockTable[BlockTableRecord.ModelSpace], OpenMode.ForRead) as BlockTableRecord;
        if (acBlockTableRecord == null) return;

        foreach (var blkId in acBlockTableRecord)
        {
            var acBlock = acTrans.GetObject(blkId, OpenMode.ForRead) as BlockReference;
            if (acBlock == null) continue;
            if (!acBlock.Name.Equals(blockName, StringComparison.CurrentCultureIgnoreCase)) continue;
            foreach (ObjectId attId in acBlock.AttributeCollection)
            {
                var acAtt = acTrans.GetObject(attId, OpenMode.ForRead) as AttributeReference;
                if (acAtt == null) continue;

                if (!acAtt.Tag.Equals(attName, StringComparison.CurrentCultureIgnoreCase)) continue;
                    
                acAtt.UpgradeOpen();
                acAtt.TextString = newValue;
            }
        }

        acTrans.Commit();
    }
}

Then from an interop AcadApplication, netload the dll and call the method from the commandline in this format:

(Command "EditBlockAtt" "BlockName" "AttributeName" "NewValue")

However if you want to go pure Interop, this may get you what you need given you have an AcadDocument object at runtime:

foreach (AcadEntity ent in acadDoc.ModelSpace)
{
    var block = ent as AcadBlockReference;
    if (block == null) continue;
    {
        if (!block.Name.Equals("BlockName", StringComparison.CurrentCultureIgnoreCase)) continue;
        var atts = block.GetAttributes() as object[];
        if (atts == null) continue;

        foreach (var attribute in atts.OfType<AcadAttributeReference>()
            .Where(attribute => attribute.TagString.Equals("AttributeName", 
                                StringComparison.CurrentCultureIgnoreCase)))
        {
            attribute.TextString = "New Value";
        }
    }
}

Also note this is using the AutoCAD 2012 Interop libraries. YMMV.