创建图元

var doc = Application.DocumentManager.MdiActiveDocument;
var ed = doc.Editor;
var db = doc.Database;

using (var docLock = doc.LockDocument())
{
    using (var tr = db.TransactionManager.StartTransaction())
    {

        var bt = tr.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;
        var btr = tr.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord;

        var txt = new DBText { TextString = "Hello World" };

        btr.AppendEntity(txt);  // 添加图元对象到数据库 + BlockTableRecord

        tr.AddNewlyCreatedDBObject(txt, true); 
        // 如果没有这行，或者 add是false 
        // 如果后面有tr.commit() ，那么图元依然会添加进数据库， 但是有问题，不能选择t


        // // 如果漏了 tr.AddNewlyCreatedDBObject(txt, true);  可以修复
        //foreach (var id in btr)
        //{
        //    var ent = tr.GetObject(id, OpenMode.ForWrite);

        //    tr.AddNewlyCreatedDBObject(ent, true); // make avaiable
        //    //ent.Erase();  // delete
        //    Console.WriteLine($"{ent}");
        //}

        // 如果用 tr.abort 那么数据会丢弃
        tr.Commit();
    }
}