dotnet-arx-development

.NET ObjectARX Development

Guide for writing correct .NET (C#) ObjectARX code using the oarx-docs MCP server.

Critical Rule

ALWAYS look up managed classes before using them. The .NET ObjectARX API wraps C++ classes with different naming and patterns.

lookup_class("Transaction", guide="arxmgd")
search_docs("adding entity to model space", guide="arxmgd_dev")

Guide Selection

• Class/method reference → arxmgd (Managed .NET Reference)
• Concepts and patterns → arxmgd_dev (Managed Developer Guide)
• C++/.NET interop → arxiop (Interop Guide)

C++ to .NET Class Mapping

When you know the C++ name but need the .NET equivalent:

lookup_class("AcDbLine", guide="arxmgd")

Common mappings:

• AcDbLine → Autodesk.AutoCAD.DatabaseServices.Line
• AcDbCircle → Autodesk.AutoCAD.DatabaseServices.Circle
• AcDbPolyline → Autodesk.AutoCAD.DatabaseServices.Polyline
• AcDbDatabase → Autodesk.AutoCAD.DatabaseServices.Database
• AcDbBlockTableRecord → Autodesk.AutoCAD.DatabaseServices.BlockTableRecord
• AcDbObjectId → Autodesk.AutoCAD.DatabaseServices.ObjectId
• AcEdCommand → Autodesk.AutoCAD.Runtime.CommandMethod (attribute)

Required Patterns

Transaction Model

All database operations must use transactions:

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTable bt = tr.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;
    BlockTableRecord btr = tr.GetObject(
        bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord;

    Line line = new Line(startPt, endPt);
    btr.AppendEntity(line);
    tr.AddNewlyCreatedDBObject(line, true);

    tr.Commit(); // ALWAYS commit
}

Command Registration

[CommandMethod("MYCOMMAND")]
public void MyCommand()
{
    Document doc = Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    Editor ed = doc.Editor;
    // ...
}

Document Locking

Required for operations from modeless dialogs or non-command contexts: