public static Rebar CreateFreeForm(
	Document doc,
	RebarBarType barType,
	Element host,
	IList<CurveLoop> curves,
	out RebarFreeFormValidationResult error
)

using Autodesk.Revit.Attributes;
using Autodesk.Revit.DB;
using Autodesk.Revit.DB.Structure;
using Autodesk.Revit.UI;
using Autodesk.Revit.UI.Selection;
using System;
using System.Collections.Generic;

namespace RebarExample.Cmds
{
    [Transaction(TransactionMode.Manual)]
    [Regeneration(RegenerationOption.Manual)]
    public class CreateFreeForm2 : IExternalCommand
    {
        public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
        {
            try
            {
                Document doc = commandData.Application.ActiveUIDocument.Document;
                if (doc == null)
                    return Result.Failed;

                //查找到钢筋类型
                FilteredElementCollector fec = new FilteredElementCollector(doc).OfClass(typeof(RebarBarType));
                if (fec.GetElementCount() <= 0)
                    return Result.Failed;
                RebarBarType barType = fec.FirstElement() as RebarBarType;

                //启动事务
                using (Transaction tran = new Transaction(doc, "CreateFreeForm2"))
                {
                    Element host = null;
                    Selection sel = commandData.Application.ActiveUIDocument.Selection;
                    try
                    {
                        //选择主体对象
                        Reference hostRef = sel.PickObject(ObjectType.Element, "Select Host");
                        host = doc.GetElement(hostRef.ElementId);
                        if (host == null)
                            return Result.Failed;
                    }
                    catch (Exception e)
                    {
                        message = e.Message;
                        return Result.Failed;
                    }

                    tran.Start();

                    this.CreateFreeForm(doc, barType, host);


                    tran.Commit();
                }
                return Result.Succeeded;
            }
            catch (Exception ex)
            {
                message = ex.Message;
                return Result.Failed;
            }
        }


        /// <summary>
        /// 创建钢筋
        /// </summary>
        /// <param name="doc"></param>
        /// <param name="barType"></param>
        /// <param name="host"></param>
        private void CreateFreeForm(Document doc, RebarBarType barType, Element host)
        {
            IList<CurveLoop> curves = new List<CurveLoop>();
            if (host is Wall wall)
            {
                //创建钢筋
                var wline = (wall.Location as LocationCurve).Curve;
                if (wline != null)
                {
                    for (var i = 0; i < 5; i++)
                    {
                        CurveLoop p = new CurveLoop();
                        var start = wline.GetEndPoint(0);
                        var end= wline.GetEndPoint(1);
                        p.Append(Line.CreateBound(new XYZ(start.X,start.Y,start.Z+i*0.1),new XYZ(end.X,end.Y,end.Z+i*0.1)));
                        curves.Add(p);
                    }
                }
            }

            RebarFreeFormValidationResult error;
            Rebar rebar = Rebar.CreateFreeForm(doc, barType, host, curves, out error);
        }
    }
}