public enum PredefinedShape : System.Enum, System.IComparable, System.IConvertible, System.IFormattable  

//Create a simple 2D rectangle graphic and apply simple fill and
//outline symbols.

//Construct on the worker thread
await QueuedTask.Run(() =>
{
  //Build 2D envelope geometry
  Coordinate2D rec_ll = new Coordinate2D(1.0, 4.75);
  Coordinate2D rec_ur = new Coordinate2D(3.0, 5.75);
  //At 2.x - Envelope rec_env = EnvelopeBuilder.CreateEnvelope(rec_ll, rec_ur);
  Envelope rec_env = EnvelopeBuilderEx.CreateEnvelope(rec_ll, rec_ur);

  //Set symbolology, create and add element to layout
  CIMStroke outline = SymbolFactory.Instance.ConstructStroke(
    ColorFactory.Instance.BlackRGB, 5.0, SimpleLineStyle.Solid);
  CIMPolygonSymbol polySym = SymbolFactory.Instance.ConstructPolygonSymbol(
    ColorFactory.Instance.GreenRGB, SimpleFillStyle.DiagonalCross, outline);

  //At 2.x - GraphicElement recElm =
  //           LayoutElementFactory.Instance.CreateRectangleGraphicElement(
  //                                                  layout, rec_env, polySym);
  //         recElm.SetName("New Rectangle");
  //
  GraphicElement recElm = ElementFactory.Instance.CreateGraphicElement(
    container, rec_env, polySym, "New Rectangle");
  //Or use Predefined shape
  GraphicElement recElm2 = ElementFactory.Instance.CreatePredefinedShapeGraphicElement(
                            container, PredefinedShape.Rectangle, rec_env, polySym, 
                            "New Rectangle2");
});

//Must be on QueuedTask.Run(() => { ...

//PredefinedShape shapeType =
//              PredefinedShape.Circle | Cloud | Cross |Circle | Triangle | ... ;

//Build geometry
Coordinate2D ll = new Coordinate2D(4, 2.5);
Coordinate2D ur = new Coordinate2D(6, 4.5);
Envelope env = EnvelopeBuilderEx.CreateEnvelope(ll, ur);

var outline = SymbolFactory.Instance.ConstructStroke(
                ColorFactory.Instance.BlueRGB, 2);
var poly_sym = SymbolFactory.Instance.ConstructPolygonSymbol(
                 null, outline);

var ge = ElementFactory.Instance.CreatePredefinedShapeGraphicElement(
                       container, shapeType, env.Center, env.Width, env.Height, 
                        poly_sym, shapeType.ToString(), true);