In this lab, we shall write code to swap group types for selected groups with other existing model group types in the Revit model. This can be done by assigning the GroupType property of the group element to some other model group type extracted using filters in Revit.

The first step would be to create a list of all the existing model group types in the Revit model. We can again use the new filtering mechanism here to create a NewLogicAndFilter type filter and set the filter based on 'GroupType' type AND family symbol name equals "Model Group".

    List<Element> elements = new List<Element>();
    Filter filterType = app.Create.Filter.NewTypeFilter( typeof( GroupType ) );
    Filter filterParam = app.Create.Filter.NewParameterFilter(
    BuiltInParameter.SYMBOL_FAMILY_NAME_PARAM, CriteriaFilterType.Equal,
    LabConstants.gsGroupTypeModel );
    Filter filterAnd = app.Create.Filter.NewLogicAndFilter( filterType, filterParam );
    app.ActiveDocument.get_Elements( filterAnd, elements );

    Dim elements As New List(Of Element)
    Dim filterType As Filter = app.Create.Filter.NewTypeFilter(GetType(GroupType))
    Dim filterParam = app.Create.Filter.NewParameterFilter(
    BuiltInParameter.SYMBOL_FAMILY_NAME_PARAM, CriteriaFilterType.Equal, LabConstants.gsGroupTypeModel)
    Dim filter As Filter = app.Create.Filter.NewLogicAndFilter(filterType, filterParam)
    Dim n As Integer = app.ActiveDocument.Elements(filter, elements)

Next, with each selected group, we will swap the group type with other model group types which we extracted using element filters in the step above. This swapping can be achieved simply by using the GroupType property of each selected group. Each group type swapping is done after confirmation from the user.

    public class Lab5_2_SwapGroupTypes : IExternalCommand
    {
      public IExternalCommand.Result Execute(
        ExternalCommandData commandData,
        ref string message,
        ElementSet elements )
        {
          Application app = commandData.Application;
          // Get all Group Types using the previous code snippet in this lab
          List<RvtElement> gts = LabUtils.GetAllModelGroupTypes( app );
          if( 0 == gts.Count )
          {
            LabUtils.ErrorMsg( "No Model Group Types in this model." );
            return IExternalCommand.Result.Cancelled;
          }
          string sMsg;
          foreach( RvtElement elem in app.ActiveDocument.Selection.Elements )
          {
            // Check for Group instance
            if( elem is Group )
            {
              Group gp = elem as Group;

              // Offer simple message box to swap the type
              // (one-by-one, stop if user confirms the change)
              foreach( GroupType gt in gts )
              {
                sMsg = "Swap OLD Type=" + gp.GroupType.Name
                  + " with NEW Type=" + gt.Name
                  + " for Group Id=" + gp.Id.Value.ToString() + "?";
                switch( LabUtils.QuestionCancelMsg( sMsg ) )
                {
                  case WinForms.DialogResult.Yes:
                    gp.GroupType = gt;
                    LabUtils.InfoMsg( "Group type successfully swapped." );
                    return IExternalCommand.Result.Succeeded;
                  case WinForms.DialogResult.Cancel:
                    LabUtils.InfoMsg( "Command cancelled!" );
                    return IExternalCommand.Result.Cancelled;
                   // just continue with the For Loop
                }
              }
            }
          }
          return IExternalCommand.Result.Succeeded;
        }
    }

    Public Class Lab5_2_SwapGroupTypes
        Implements IExternalCommand
        Public Function Execute(ByVal commandData As Autodesk.Revit.ExternalCommandData, ByRef message As String, ByVal elements As Autodesk.Revit.ElementSet) As Autodesk.Revit.IExternalCommand.Result Implements Autodesk.Revit.IExternalCommand.Execute

            Dim app As Revit.Application = commandData.Application

            ' First get all Group Types of Model Family
            'Get all Group Types using the previous code snippet in this lab
            Dim gts As List(Of Element) = LabUtils.GetAllModelGroupTypes(app)
            'Dim gts As ElementSet = LabUtils.GetAllGroupTypes(app)

            If gts.Count = 0 Then
                MsgBox("No Model Group Types in this model!")
                Return IExternalCommand.Result.Cancelled
            End If

            ' Loop through selection
            Dim elem As Revit.Element
            If (app.ActiveDocument.Selection.Elements.Size = 0) Then
                MsgBox("No Group has been selected!")
            Else
                For Each elem In app.ActiveDocument.Selection.Elements

                    ' Check for Group instance
                    If TypeOf elem Is Group Then
                        Dim gp As Group = elem

                        ' Offer simple message box to swap the type
                        ' (one-by-one, stop if user confirms the change)
                        Dim gt As GroupType
                        For Each gt In gts
                            Select Case (MsgBox("Swap OLD Type=" & gp.GroupType.Name & " with NEW Type=" & gt.Name & " for Group Id=" & gp.Id.Value.ToString & "?", MsgBoxStyle.YesNoCancel))
                                Case MsgBoxResult.Yes
                                    gp.GroupType = gt
                                    MsgBox("Group type successfully swapped!")
                                    Exit For
                                Case MsgBoxResult.Cancel
                                    MsgBox("Command cancelled!")
                                    Return IExternalCommand.Result.Cancelled
                                Case MsgBoxResult.No
                                    ' just continue with the For Loop
                            End Select
                        Next
                    End If

                Next
            End If

            Return IExternalCommand.Result.Succeeded
        End Function
    End Class

Build the project, adjust the ini file and examine the output in a model with various pre-existing model group types.