using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Windows.Forms;

using System.Text;

using Autodesk.Navisworks.Api.Controls;

      static public void IteratePropertyCategories()
      {
         //create a list to store the category names
         List<string> uniqueCategories = new List<string>();

         //check there is a valid ActiveDocument
         if (Autodesk.Navisworks.Api.Application.ActiveDocument != null &&
            !Autodesk.Navisworks.Api.Application.ActiveDocument.IsClear)
         {
            //iterate the ModelItems in the current selection
            foreach (ModelItem item in Autodesk.Navisworks.Api.Application.ActiveDocument.CurrentSelection.SelectedItems)
            {
               //iterate the item's PropertyCategory entries
               foreach (PropertyCategory category in item.PropertyCategories)
               {
                  string text = string.Format("{0} / {1}", category.DisplayName, category.Name);
                  //check name isnt already in the list
                  if (!uniqueCategories.Contains(text))
                  {
                     //add to the list
                     uniqueCategories.Add(text);
                  }
               }
            }

            //build a display string
            StringBuilder output = new StringBuilder();
            foreach (string s in uniqueCategories)
               output.AppendLine(s);

            //output to the screen
            MessageBox.Show(output.ToString());
         }
      }