Revit二次开发—载入族并交互式放置

using (Transaction tx = new Transaction(doc))
{
    tx.Start("Transaction Name");
    Family family = null;
    var str = "xxx.rfa";
    doc.LoadFamily(str, out family);
    tx.Commit();
    // 交互式放置之前需要结束事务
    if (family != null)
    {
      var symbol = doc.GetElement(family.GetFamilySymbolIds().FirstOrDefault()) as FamilySymbol
        uidoc.PromptForFamilyInstancePlacement(symbol);
    }
}

try
{
}
catch (Exception ex)
{
    //用户取消异常，不抛出异常信息
    if (!(ex is Autodesk.Revit.Exceptions.OperationCanceledException))
    {
        throw ex;
    }
}

Family family = null;
// 过滤当前文档是否存在该族
FilteredElementCollector collector = new FilteredElementCollector(doc);
collector.OfClass(typeof(Family));
IList<Element> CollectorList = collector.ToElements();
foreach (var elem in CollectorList)
{
    var familyItem = elem as Family;
    // str是要载入族的名称
    if (familyItem.Name == Path.GetFileNameWithoutExtension(str))
    {
        family = familyItem;
        break;
    }
}
// 如果未载入过，则载入该族
if (family == null)
{
    doc.LoadFamily(str, out family);
}
// 交互式放置
uidoc.PromptForFamilyInstancePlacement(
doc.GetElement(family.GetFamilySymbolIds().FirstOrDefault()) as FamilySymbol);