您好，请帮我看看这段代码，为什么老是有这个错误提示：Attempt to modify the model outside of transaction.

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

namespace addWall
{
[Transaction(TransactionMode.Manual)]
[Regeneration(RegenerationOption.Manual)]
public class add:IExternalCommand
{
public Wall CreateWallUsingCurve1(Autodesk.Revit.DB.Document document, Level level)
{
// Build a location line for the wall creation
XYZ start = new XYZ(0, 0, 0);
XYZ end = new XYZ(10, 10, 0);
Line geomLine = document.Application.Create.NewLineBound(start, end);

// Create a wall using the location line
return document.Create.NewWall(geomLine, level, true);
}

Result IExternalCommand.Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
{

UIDocument uidoc = commandData.Application.ActiveUIDocument;
ElementSet selections = uidoc.Selection.Elements;
Document doc = uidoc.Document;
Level lv=null;
foreach(Element elem in selections)
{
lv=elem.Level;
break;
}
try
{
CreateWallUsingCurve1(doc, lv);
}
catch(Exception e)
{

message = e.Message;
return Result.Failed;

}

return Result.Succeeded;
}

}
}

问题解决了，非常非常感谢博主的解答，你真是大好人！！！

Thanks for you help! You are a big good man!!!! 哈哈，俺不会英文……