BuildingCoder.CmdListViews.Execute C# (CSharp) Method

        public Result Execute(
            ExternalCommandData commandData,
            ref string message,
            ElementSet elements)
        {
            UIApplication app = commandData.Application;
              Document doc = app.ActiveUIDocument.Document;

              FilteredElementCollector sheets
            = new FilteredElementCollector( doc );

              sheets.OfClass( typeof( ViewSheet ) );

              // map with key = sheet element id and
              // value = list of viewport element ids:

              Dictionary<ElementId, List<ElementId>>
            mapSheetToViewport =
            new Dictionary<ElementId, List<ElementId>>();

              // map with key = viewport element id and
              // value = sheet element id:

              Dictionary<ElementId, ElementId>
            mapViewportToSheet =
            new Dictionary<ElementId, ElementId>();

              foreach( ViewSheet sheet in sheets )
              {
            //int n = sheet.Views.Size; // 2014

            ISet<ElementId> viewIds = sheet.GetAllPlacedViews(); // 2015

            int n = viewIds.Count;

            Debug.Print(
              "Sheet {0} contains {1} view{2}: ",
              Util.ElementDescription( sheet ),
              n, Util.PluralSuffix( n ) );

            ElementId idSheet = sheet.Id;

            int i = 0;

            foreach( ElementId id in viewIds )
            {
              View v = doc.GetElement( id ) as View;

              BoundingBoxXYZ bb;

              bb = v.get_BoundingBox( doc.ActiveView );

              Debug.Assert( null == bb,
            "expected null view bounding box" );

              bb = v.get_BoundingBox( sheet );

              Debug.Assert( null == bb,
            "expected null view bounding box" );

              Element viewport = GetViewport( sheet, v );

              // null if not in active view:

              bb = viewport.get_BoundingBox( doc.ActiveView );

              BoundingBoxUV outline = v.Outline;

              Debug.WriteLine( string.Format(
            "  {0} {1} bb {2} outline {3}",
            ++i, Util.ElementDescription( v ),
            (null == bb ? "<null>" : Util.BoundingBoxString( bb )),
            Util.BoundingBoxString( outline ) ) );

              if( !mapSheetToViewport.ContainsKey( idSheet ) )
              {
            mapSheetToViewport.Add( idSheet,
              new List<ElementId>() );
              }
              mapSheetToViewport[idSheet].Add( v.Id );

              Debug.Assert(
            !mapViewportToSheet.ContainsKey( v.Id ),
            "expected viewport to be contained"
            + " in only one single sheet" );

              mapViewportToSheet.Add( v.Id, idSheet );
            }
              }
              return Result.Cancelled;
        }