assets/samples/Samples/ContextualAnalyticalModel/CS/Utilities.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Autodesk.Revit;
using Autodesk.Revit.DB;
using Autodesk.Revit.UI;
using Autodesk.Revit.DB.Structure;
using Autodesk.Revit.UI.Selection;

namespace ContextualAnalyticalModel
{
   /// <summary>
   /// Utility methods
   /// </summary>
   public static class Utilities
   {
      /// <summary>
      /// Selects a Revit element and returns its ElementId
      /// </summary>
      /// <param name="uiDoc">UIDocument</param>
      /// <param name="msg">status message</param>
      /// <returns>ElementId of the selected element</returns>
      public static ElementId GetSelectedObject(UIDocument uiDoc, string msg)
      {
         ElementId selectedElementId = ElementId.InvalidElementId;
         Reference refElem = uiDoc.Selection.PickObject(ObjectType.Element, msg);
         if (refElem != null)
         {
            selectedElementId = refElem.ElementId;
         }

         return selectedElementId;
      }

      /// <summary>
      /// Selects multiple Revit elements and returns the ElementIds
      /// </summary>
      /// <param name="uiDoc">UIDocument</param>
      /// <param name="msg">status message</param>
      /// <returns>List of ElementId of the selected elements</returns>
      public static ISet<ElementId> GetSelectedObjects(UIDocument uiDoc, string msg)
      {
         ISet<ElementId> selectedElementIdList = new HashSet<ElementId>();
         IList<Reference> refElemList = uiDoc.Selection.PickObjects(ObjectType.Element, msg);
         if (refElemList != null)
         {
            selectedElementIdList = refElemList.Select(x => x.ElementId).ToHashSet();
         }

         return selectedElementIdList;
      }
   }
}