assign material to directshape via paint

seems it's not working.

I tried 2017 new ShapeImporter to create DirectShape element, works fine, but doesn't work when using Document.Paint, is it because I have to use it before or during creating DirectShape? if so then how to get Element Id, I mean e.Id of doc.Paint(e.Id, face, mat.Id) in which e is newly created DirectShape element.

besides, still no way to directly assign material to DirectShape element?