用autocad.net写一个插件，当添加对象时，获取对象的objectid

可以使用以下代码来实现：

using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;

namespace MyPlugin
{
    public class MyCommands
    {
        [CommandMethod("AddObject")]
        public void AddObject()
        {
            Document doc = Application.DocumentManager.MdiActiveDocument;
            Database db = doc.Database;
            Editor ed = doc.Editor;

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

                // 添加对象
                Circle circle = new Circle(new Point3d(0, 0, 0), Vector3d.ZAxis, 1);
                btr.AppendEntity(circle);
                tr.AddNewlyCreatedDBObject(circle, true);

                // 获取对象的objectid
                ObjectId objectId = circle.ObjectId;

                tr.Commit();
            }
        }
    }
}

当执行 `AddObject` 命令时，会在当前图形中添加一个圆形，并获取该圆形的 `ObjectId`。