Revit更改用户选择

private void ChangeSelection(Document document)
{
     UIDocument uidoc = new UIDocument(document);
     Autodesk.Revit.UI.Selection.SelElementSet collection = uidoc.Selection.Elements;
     TaskDialog.Show("Revit","Number of selected elements: " + collection.Size.ToString());
     SelElementSet newSelectedElementSet = SelElementSet.Create();
     foreach (Autodesk.Revit.DB.Element elements in collection)
     {
	     if (elements is Wall)
	     {
		     newSelectedElementSet.Add(elements);
	     }
     }
     uidoc.Selection.Elements = newSelectedElementSet;
     if (0 != newSelectedElementSet.Size)
     {
	     TaskDialog.Show("Revit",uidoc.Selection.Elements.Size.ToString() +  " Walls are selected!");
     }
     else
     {
	      TaskDialog.Show("Revit","No Walls have been selected!");
     }
}