dst.CurrentStyle有误，请检查

非常抱歉，是我的疏忽导致了错误。正确的写法应该是 `db.Dimstyle`。以下是修改后的代码：

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

namespace GetCurrentDimensionStyleName
{
    public class Commands
    {
        [CommandMethod("GetCurrentDimensionStyleName")]
        public static void GetCurrentDimensionStyleName()
        {
            Document doc = Application.DocumentManager.MdiActiveDocument;
            Editor ed = doc.Editor;
            Database db = doc.Database;

            using (Transaction tr = db.TransactionManager.StartTransaction())
            {
                DimStyleTable dst = tr.GetObject(db.DimStyleTableId, OpenMode.ForRead) as DimStyleTable;
                DimStyleTableRecord currentDst = tr.GetObject(db.Dimstyle, OpenMode.ForRead) as DimStyleTableRecord;

                ed.WriteMessage("\nCurrent default dimension style name: " + currentDst.Name);

                tr.Commit();
            }
        }
    }
}

该代码获取当前文档、编辑器和数据库，然后在事务中获取当前的标注样式表和默认标注样式记录，并输出当前默认标注样式的名称。