Visual Basic

Option Explicit On
Imports Microsoft.Office.Core
Imports Extensibility

Public Class Connect
    Implements IDTExtensibility2

    Public ext_cm_Startup As ext_ConnectMode
    Public ext_dm_HostShutdown As ext_DisconnectMode
    Public edlcaption As String = ChrW(&H3B1) & ChrW(&H3A9) & "-ED&L"

    Dim oHostApp As Object
    Dim WithEvents MyButton As CommandBarButton

    Private Sub IDTExtensibility2_OnConnection(ByVal Application As Object, ByVal ConnectMode As ext_ConnectMode, _
                                               ByVal AddInInst As Object, ByRef custom As System.Array) _
                                               Implements IDTExtensibility2.OnConnection

        On Error Resume Next
        ' Set a reference to the host application...
        oHostApp = Application

        ' If you aren't in startup, then manually call OnStartupComplete...
        If (ConnectMode <> ext_cm_Startup) Then _
           Call IDTExtensibility2_OnStartupComplete(custom)

    End Sub

    Private Sub IDTExtensibility2_OnStartupComplete(ByRef custom As System.Array) Implements IDTExtensibility2.OnStartupComplete
        Dim oCommandBars As Microsoft.Office.Core.CommandBars
        Dim oStandardBar As Microsoft.Office.Core.CommandBar

        On Error Resume Next
        ' Set up a custom button on the "Standard" commandbar...
        oCommandBars = oHostApp.CommandBars
        If oCommandBars Is Nothing Then
            ' Outlook has the CommandBars collection on the Explorer object
            oCommandBars = oHostApp.ActiveExplorer.CommandBars
        End If

        oStandardBar = oCommandBars.Item("Standard")
        If oStandardBar Is Nothing Then
            ' Access names it's main toolbar Database
            oStandardBar = oCommandBars.Item("Database")
        End If

        ' In case the button was not deleted, use the exiting one...
        MyButton = oStandardBar.Controls.Item(edlcaption)
        If MyButton Is Nothing Then

            MyButton = oStandardBar.Controls.Add(1)
            With MyButton
                .Caption = edlcaption
                .Style = MsoButtonStyle.msoButtonCaption
                .Tag = "EDL"

                .OnAction = "!<MyCOMAddin.Connect>"
                .Visible = True
            End With
        End If

        ' Display a simple message to know which application you started in...
        MsgBox("Started in " & oHostApp.Name & ".")

        oStandardBar = Nothing
        oCommandBars = Nothing
    End Sub

    Private Sub IDTExtensibility2_OnDisconnection(ByVal RemoveMode As Extensibility.ext_DisconnectMode, ByRef custom As System.Array) _
    Implements IDTExtensibility2.OnDisconnection

        On Error Resume Next
        If RemoveMode <> ext_dm_HostShutdown Then _
           Call IDTExtensibility2_OnBeginShutdown(custom)

        oHostApp = Nothing

    End Sub

    Private Sub IDTExtensibility2_OnBeginShutdown(ByRef custom As System.Array) Implements IDTExtensibility2.OnBeginShutdown
        On Error Resume Next
        ' Notify the user you are shutting down, and delete the button...
        MsgBox(String.Format("Der Button '{0}' wird gelöscht.", MyButton.Caption))
        MyButton.Delete()
        MyButton = Nothing
    End Sub

    Private Sub IDTExtensibility2_OnAddInsUpdate(ByRef custom As System.Array) Implements IDTExtensibility2.OnAddInsUpdate
        'You do nothing if this is called, but you need to
        'add a comment so Visual Basic properly implements the function...
    End Sub

    Private Sub MyButton_Click1(ByVal Ctrl As Microsoft.Office.Core.CommandBarButton, ByRef CancelDefault As Boolean) Handles MyButton.Click
        MsgBox("Hier wird eine Aktion vom Add-In ausgeführt!")
    End Sub

    Private Function listFiles(ByVal dir As String) As List(Of String)

        Return Nothing
    End Function
End Class

regasm MyCOMAddIn.dll /codebase /tlb=MyCOMAddIn.tlb
Gacutil /if MyCOMAddIn.dll

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Office\Excel\Addins\MyComAddin.Connect]
"LoadBehavior"=dword:00000003
"CommandLineSafe"=dword:00000000
"FriendlyName"="MyComAddin Connect Class"
"Description"="MyComAddin Connect Class"