Hi explosive 369, you cannot use the code in the way you do. First, formula parameters are *family* related, meaning that you define them when editing families. In project context, there are no formula parameters (as far as I know). Second, syntax for formula parameters is different from the code we use in API:
http://wikihelp.autodesk.com/Revit/enu/Community/Tips_and_Tricks/Families%2c_Parameters%2c_Formulas/... In formulas, you can refer to other exposed parameters but not to internal element properties (like the Id). So I would suggest you to implement a little add-in or macro for filling your test_id parameter values *programmatically*. You cannot perform this otherwise. Since this is the Revit *API* forum, you are on the right place here
😉 Get all the door instances, and for each door of them do: door.get_Parameter("test_id").Set(door.Id.IntegerValue); Make sure that each door you access already *has* this parameter at all before trying to set it. Ah, i see that your "test_id" parameter must be an *instance* parameter, not a *type* parameter, since each element has an *individual* Id value, of course. For filtering elements performantly, please look at the Revit SDK samples or visit The Building Coder:
http://thebuildingcoder.typepad.com/ Hope this helpes you. Best regards, Revitalizer