List Railing Types

This is in response to a query from Berria on iterating over the railing types in the model. It is also once again about teaching how to fish, and not just feeding people, at least I hope so. If I want to list all the railing types, the best way to go is probably to define an API filter which retrieves them from the model for me. How do I design that filter? I start by opening a new model, inserting a railing, and examining it with RvtMgdDbg. There I can easily determine that its built-in category is OST_StairsRailing. Therefore, I first thought that an API filter selecting all family symbols of this category should suffice. The project browser shows me the following stair and railing symbols in my current model:

I implemented a new external command CmdListRailingTypes to test this approach, with the following code:

Application app = commandData.Application;
Document doc = app.ActiveDocument;
CreationFilter cf = app.Create.Filter;
 
List<Element> symbols = new List<Element>();
 
BuiltInCategory bic 
  = BuiltInCategory.OST_StairsRailing;
 
Filter f1 
  = cf.NewCategoryFilter( bic );
 
Filter f2 
  = cf.NewTypeFilter( typeof( FamilySymbol ) );
 
doc.get_Elements( f, symbols );

foreach( FamilySymbol s in symbols )
{
  Debug.Print(
    "Family name={0}, symbol name={1}",
    s.Family.Name, s.Name );
}
return CmdResult.Failed;

It makes use of a new alias for CreationFilter:

using CreationFilter
  = Autodesk.Revit.Creation.Filter;

To my initial surprise, no symbols were found. I thereupon took a closer look at the symbols within the railings family in RvtMgdDbg and discovered that the category of the M_Baluster symbols is not OST_StairsRailing but OST_StairsRailingBaluster. Changing the value of the 'bic' variable to that built-in category returns some valid results:

Family name=M_Baluster - Square, symbol name=25mm
Family name=M_Baluster - Square, symbol name=20mm
Family name=M_Baluster - Round, symbol name=25mm
Family name=M_Baluster - Round, symbol name=20mm

This does still not include all the railing symbols listed in the browser, so I went back into RvtMgdDbg and searched for those as well. They were not listed in the FamilySymbol collection, but under Symbols, this time indeed with the category OST_StairsRailing.

Making use of this info, I implemented a second filter and iteration to retrieve and list Symbol objects like this:

bic = BuiltInCategory.OST_StairsRailing;
f1 = cf.NewCategoryFilter( bic );
f2 = cf.NewTypeFilter( typeof( Symbol ) );
f = cf.NewLogicAndFilter( f1, f2 );
 
doc.get_Elements( f, symbols );
 
n = symbols.Count;
 
Debug.Print( "{0}"
  + " OST_StairsRailing symbol{1}:",
  n, Util.PluralSuffix( n ) );
 
foreach( Symbol s in symbols )
{
  FamilySymbol fs = s as FamilySymbol;
 
  Debug.Print(
    "Family name={0}, symbol name={1}",
    null == fs ? "<none>" : fs.Family.Name, 
    s.Name );
}

The result of this code is somewhat surprising too. The non-family symbols that we are looking for are retrieved now, just like we hoped, and we also retrieve the family symbols that we already saw above:

6 OST_StairsRailing symbols:
Family name=M_Baluster - Square, symbol name=25mm
Family name=M_Baluster - Square, symbol name=20mm
Family name=M_Baluster - Round, symbol name=25mm
Family name=M_Baluster - Round, symbol name=20mm
Family name=<none>, symbol name=900mm Pipe
Family name=<none>, symbol name=900mm Rectangular

This goes to show several things:

• You need to explore the model.
• You may get unexpected results.

I'll just leave it at that for now.

Here is version 1.0.0.25 of the complete Visual Studio solution with the new CmdListRailingTypes command implementation.