Excel VSTO Addin イベント消失 改修案

Public Class ThisAddIn
    Private eventWorksheets As List(Of Excel.Worksheet)

    Private Sub ThisAddIn_Startup() Handles Me.Startup
        ' ワークブックアクティブイベント登録
        AddHandler Globals.ThisAddIn.Application.WorkbookActivate, New Excel.AppEvents_WorkbookActivateEventHandler(AddressOf add_handlers_to_book)
    End Sub

    Private Sub add_handlers_to_book(workbook As Excel.Workbook)
        Me.eventWorksheets = New List(Of Excel.Worksheet)
        For Each worksheet As Excel.Worksheet In workbook.Worksheets
            If worksheet.Name = "Sheet2" Or worksheet.Name = "Sheet3" Then
                ' シート名が Sheet2かSheet3の場合、イベント登録
                AddHandler worksheet.SelectionChange, New Excel.DocEvents_SelectionChangeEventHandler(AddressOf selection_change)
                ' イベントを設定したワークシートを保持
                Me.eventWorksheets.Add(worksheet)
            End If
        Next
    End Sub

    Private Sub selection_change(target As Excel.Range)
        Dim worksheet As Excel.Worksheet = target.Worksheet
        worksheet.Cells(1, 1).Value = target.Address

        GC.Collect()
    End Sub

End Class