vb.net get group extents

Imports System.Collections.Generic
Imports Autodesk.AutoCAD.Runtime
Imports Autodesk.AutoCAD.EditorInput
Imports Autodesk.AutoCAD.DatabaseServices
Imports Autodesk.AutoCAD.ApplicationServices
Namespace GroupExtents
    Public Shared Class TransactionExtensions
        ' A simple extension method that aggregates the extents of any entities
        ' passed in (via their ObjectIds)
        <System.Runtime.CompilerServices.Extension> _
        Public Shared Function GetExtents(tr As Transaction, ids As ObjectId()) As Extents3d
            Dim ext As New Extents3d()
            For Each id As Object In ids
                Dim ent As Object = TryCast(tr.GetObject(id, OpenMode.ForRead), Entity)
                If ent IsNot Nothing Then
                    ext.AddExtents(ent.GeometricExtents)
                End If
            Next
            Return ext
        End Function
    End Class
    Public Class Commands
        <CommandMethod("GE")> _
        Public Sub GroupExtents()
            Dim doc As Object = Application.DocumentManager.MdiActiveDocument
            Dim db As Object = doc.Database
            Dim ed As Object = doc.Editor
            Using tr As Object = db.TransactionManager.StartTransaction()
                ' Get the group dictionary from the drawing
                Dim gd As DBDictionary = CType(tr.GetObject(db.GroupDictionaryId, OpenMode.ForRead), DBDictionary)
                If gd.Count = 0 Then
                    ed.WriteMessage(vbLf & "No groups found in drawing.")
                Else
                    ' List the groups in the drawing with an index
                    Dim groupNames As New List(Of String)(gd.Count)
                    ed.WriteMessage(vbLf & "Groups:")
                    Dim i As Integer = 0
                    For Each entry As Object In gd
                        i += 1
                        ed.WriteMessage(vbLf & "{0}. {1}", i, entry.Key)
                        groupNames.Add(entry.Key)
                    Next
                    ' Ask the user to select a group number
                    Dim pio As New PromptIntegerOptions(vbLf & "Enter group index")
                    pio.AllowNegative = False
                    pio.AllowZero = False
                    pio.DefaultValue = 1
                    pio.LowerLimit = 1
                    pio.UpperLimit = i
                    Dim pir As Object = ed.GetInteger(pio)
                    If pir.Status = PromptStatus.OK Then
                        ' Get the selected group
                        Dim grp As Object = TryCast(tr.GetObject(CType(gd(groupNames(pir.Value - 1)), ObjectId), OpenMode.ForRead), Group)
                        If grp IsNot Nothing Then
                            ' Call our extension method to get the extents of the group's
                            ' referenced objects
                            Dim ext As Object = tr.GetExtents(grp.GetAllEntityIds())
                            ' Print the information for the user
                            ed.WriteMessage(vbLf & "Group's extents are from {0} to {1}.", ext.MinPoint, ext.MaxPoint)
                        End If
                    End If
                End If
                ' Commit the transaction
                tr.Commit()
            End Using
        End Sub
    End Class
End Namespace