Can't use C# standard Dictionary as container for AutoCAD API TypedValue and ExtendedData ResultBuffer

Question

public class MyApp
{

    [CommandMethod("ADDXDATA")]
    static public void AddXdata()
    
    {
        Document doc = Application.DocumentManager.MdiActiveDocument;
        Database db = doc.Database;
        Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;
    
        try
        {
            using (Transaction tr = db.TransactionManager.StartTransaction())
            {
                PromptEntityResult ers = ed.GetEntity("Pick entity ");
    
                Entity ent = (Entity)tr.GetObject(ers.ObjectId, OpenMode.ForWrite);
    
                RegAppTable regTable = (RegAppTable)tr.GetObject(db.RegAppTableId, OpenMode.ForRead);
    
                if (!regTable.Has("TESTEAPP"))
                {
                    regTable.UpgradeOpen();
                    RegAppTableRecord app = new RegAppTableRecord();
                    app.Name = "TESTEAPP";
                    regTable.Add(app);
                    tr.AddNewlyCreatedDBObject(app, true);
                }
    
                Dictionary<DxfCode, object> xd = new Dictionary<DxfCode, object>
                {
                    { DxfCode.ExtendedDataRegAppName, "TESTEAPP" },
                    { DxfCode.ExtendedDataInteger16, 1000 }
                };
    
                List<TypedValue> tvslist = new List<TypedValue>();
                foreach (var key in xd.Keys)
                {
                    tvslist.Append(new TypedValue((int)key, xd[key]));
                }
                TypedValue[] tvs = tvslist.ToArray();
    
                ResultBuffer rb = new ResultBuffer(tvs);
    
                ent.XData = rb;
                tr.Commit();
            }
        }
    
        catch (Exception ex)
        {
            Application.ShowAlertDialog(ex.Message);
        }
    }

}

I'm trying to use a standard C# dictionary as a container for passing AutoCAD API TypedValue for the .Xdata property get. If I just put the TypedValue array directly inside the

new ResultBuffer(new TypedValue(DxfCode.ExtendedDataRegAppName, "TESTEAPP"), new TypedValue(DxfCode.ExtendedDataInteger16, 1000)); it works just fine, whats makes no sense. What am I missing, any thoughts?

Answer 1

I get it! Seems I trying to use the LINQ .Append() on a List, and that's was not working. Use .Add() instead. Now I am studying more about LINQ, because it can be tricky sometimes.

Replaced:

tvslist.Append(new TypedValue((int)key, xd[key]));

With:

tvslist.Add(new TypedValue((int)key, xd[key]));

And worked just fine.

The LINQ Append(element) always returns a new IEnumeable with the element appended on tail. And here, I wanted modify the existent List so the .Add() its the right way. More on the diference about Append() and Add() can be found here: Difference between a List's Add and Append method?