We have looked at many aspects of categories in the past, such as category comparison, family categories, categories and parameter bindings, and system versus user defined categories.

Here is very basic question that just came in and may be of general interest:

Question: Is it possible to obtain a complete list of Revit family categories?

Answer: Yes, sure it is. You can create it yourself. There are two sets of categories in a Revit project document: the ones defined in the document itself, and the pre-defined built-in ones.

The top-level document ones are available from the document settings categories property, and the built-in ones from the BuiltInCategory enumeration.

I implemented a new Building Coder sample command CmdCategories to list the contents of these two collections.

This is the code to read the document categories. The Categories object is a map that contains all the top-level Category objects within the Document:

  UIApplication app = commandData.Application;
  Document doc = app.ActiveUIDocument.Document;
  Categories categories = doc.Settings.Categories;
  int n = categories.Size;
  Debug.Print( "{0} categories and their parents:", n );
  foreach( Category c in categories )
    Category p = c.Parent;
    Debug.Print( "  {0} ({1}), parent {2}",
      c.Name, c.Id.IntegerValue, 
      (null == p ? "<none>" : p.Name) );

This lists 219 categories in the sample project I tested it in, starting like this:

219 categories and their parents:
  Plumbing Fixture Tags (-2005010), parent <none>
  Switch System (-2008101), parent <none>
  Structural Framing Tags (-2005015), parent <none>
  Room Tags (-2000480), parent <none>
  Raster Images (-2000560), parent <none>
  Security Devices (-2008079), parent <none>
  Structural Beam System Tags (-2005130), parent <none>

Since all of these are top-level categories, the Parent property is always null. You can still ask the map for a sub-category by name or id and it should return it to you. You can also extract the sub-categories of each parent category you iterate.

Here is the code iterating over the built-in categories listed in the BuiltInCategory enumeration:

  Array bics = Enum.GetValues( 
    typeof( BuiltInCategory ) );
  n = bics.Length;
  Debug.Print( "{0} built-in categories and the "
    + "corresponding document ones:", n );
  Category cat;
  string s;
  foreach( BuiltInCategory bic in bics )
      cat = categories.get_Item( bic );
      s = (null == cat)
        ? "<none>"
        : string.Format( "--> {0} ({1}", 
          cat.Name, cat.Id.IntegerValue );
    catch( Exception ex )
      s = ex.GetType().Name + " " + ex.Message;
    Debug.Print( "  {0} {1}", bic.ToString(), s );

This lists 747 built-in categories and their corresponding document ones, if found.

I had to add an exception handler around the call to the Categories collection Item property taking a BuiltInCategory argument, since I discovered that it throws exceptions when called with certain built-in categories:

This is due to the fact that a few categories can't be stored in the map correctly because their names are the same as other categories, and the name is used as a key. A workaround might be: obtain the category from a new Categories object (from Settings.Categories), get the category directly by BuiltInCategory from that object.

Here is a text file including the output of running this command in my simple sample project.

Here is version 2011.0.67.0 of The Building Coder sample source code and Visual Studio solution including the new command.

The Revit 2010 version of the Revit API introduction labs also included a command Lab2_5_Categories which performed some further analysis on the document and built-in categories and their relationships with each other. The last version we published was in the discussion on selecting model elements .