Public Class start
 
    Dim subform1 As New dialogform
 
    'Kann auch im Designer erstellt werden 
    Dim WithEvents menustrip1 As New MenuStrip With {.Parent = Me}
    Dim WithEvents mainmenu As New ToolStripMenuItem
    Dim WithEvents showsubform As New Button With _
    {.Parent = Me, .Text = "Show Subform", .Top = 40}
 
    Private Sub start_Load(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles MyBase.Load
 
        mainmenu.Text = "MainMenu"
        mainmenu.Name = "keyofmainmenu"
        menustrip1.Items.Add(mainmenu)
    End Sub
 
    Private Sub showsubform_Click(ByVal sender As Object, _
                  ByVal e As System.EventArgs) Handles showsubform.Click
        subform1.MainFormMenuStrip = menustrip1 'Übergabe der Menureferenz
        subform1.ShowDialog()  
    End Sub
End Class

Public Class dialogform
 
    Dim WithEvents checkitem As New Button With _
    {.Parent = Me, .Text = "Check Menu Item", .Width = 200}
 
    Dim _MenuStrip As MenuStrip
 
    Public Property MainFormMenuStrip() As MenuStrip
        Set(ByVal value As MenuStrip)
            _MenuStrip = value
        End Set
        Get
            Return _MenuStrip
        End Get
    End Property
 
    Private Sub checkitem_Click(ByVal sender As Object, _
        ByVal e As System.EventArgs) Handles checkitem.Click
 
        If _MenuStrip Is Nothing Then Exit Sub
        Dim mainmenu_index As Integer = _MenuStrip.Items.IndexOfKey( _
          "keyofmainmenu")
        If mainmenu_index < 0 Then Exit Sub
 
        Dim mainmenu As ToolStripMenuItem = _
            CType(_MenuStrip.Items(mainmenu_index), ToolStripMenuItem)
 
        If mainmenu.DropDownItems.ContainsKey("keyofsubitem") Then Exit Sub
 
        Dim subitem As New ToolStripMenuItem
        subitem.Text = "Sub Item"
        subitem.Name = "keyofsubitem"
        mainmenu.DropDownItems.Add(subitem)
    End Sub
End Class

'Zunächst ein Item erstellen
Dim tsi As New ToolStripMenuItem
tsi.Text = "Item1"
tsi.Name = "Key1"   'Name fungiert auch als Key
 
'Menustrip erstellen
Dim ms As New MenuStrip
'Das Item hinzufügen
ms.Items.Add(tsi)
 
'Items-Auflistung (ToolStripItemCollection) durchsuchen ....
 
'Suche nach der Referenz auf das Item
If ms.Items.Contains(tsi) Then
  Dim index As Integer = ms.Items.IndexOf(tsi)
  MsgBox("Item ist im Menü bereits enthalten: " & CStr(index))
End If
 
'Suche nach dem Item-Schlüssel
If ms.Items.ContainsKey("Key1") Then
   Dim index As Integer = ms.Items.IndexOfKey("Key1")
   MsgBox("Schlüssel ist im Menü bereits enthalten:" & CStr(index))
End If
 
'Suche nach dem Text
For i As Integer = 0 To ms.Items.Count - 1
   If ms.Items(i).Text.ToUpper.Trim = "ITEM1" Then
      MsgBox("Text ist im Menü bereits enthalten")
      Exit For
   End If
Next i

        Dim tsi As New ToolStripMenuItem
        tsi.Name = "test"   'Name fungiert auch als Key
 
        If start.MenuStrip1.Items.Contains(tsi) Then
            Dim index As Integer = start.MenuStrip1.Items.IndexOf(tsi)
            MsgBox("Item ist im Menü bereits enthalten: " & CStr(index))
        End If

    MenuStrip1.Items.Add(tsi)

    If MenuStrip1.Items.ContainsKey(tsi.Name) Then

    If MenuStrip1.Items(tsi.Name) IsNot Nothing Then

________
Alle Angaben ohne Gewähr. Keine Haftung für Vorschläge, Tipps oder sonstige Hilfe, falls es schiefgeht, nur Zeit verschwendet oder man sonst nicht zufrieden ist

        'Prüfen ob Hauptmenüelemt vorhanden ist
        If start.MenuStrip1.Items.ContainsKey(mainmenu.Name) = True Then
            Dim mainindex As Integer = start.MenuStrip1.Items.IndexOf(mainmenu)
            MsgBox("Hauptmenü Item ist im Menü bereits enthalten: " & CStr( _
              mainindex))
 
            Dim MenItem As ToolStripMenuItem = CType(mainmenu, _
              ToolStripMenuItem)
            'Prüft ob Submenüelemt vorhanden
            If MenItem.DropDownItems.ContainsKey(submenu.Name) = True Then
                Dim subindex As Integer = MenItem.DropDownItems.IndexOf(submenu)
                MsgBox("Untermenü Item ist im Menü bereits enthalten: " & CStr( _
                  subindex))
            Else
                MenItem.DropDownItems.Add(mit(1))
            End If
        End If

Dim MenItem As ToolStripMenuItem = CType(mainmenu, ToolStripMenuItem)

Dim menustrip1 As New MenuStrip
Dim mainmenu As New ToolStripMenuItem
Dim submenu As New ToolStripMenuItem
 
'Auskommentieren dieser Zeile(n) entscheidet darüber, 
'welche Bedingung gegeben ist
mainmenu.DropDownItems.Add(submenu)
menustrip1.Items.Add(mainmenu)
 
 
If menustrip1.Items.Contains(mainmenu) Then
   If mainmenu.DropDownItems.Contains(submenu) Then
      MsgBox("Submenu ist im Dropdown des Mainmenu bereits vorhanden")
   Else
      mainmenu.DropDownItems.Add(submenu)
   End If
Else
   MsgBox("Mainmenu ist im Menustrip nicht enthalten")
End If

Dim mainmenu_itemindex As Integer = menustrip1.Items.IndexOf(mainmenu)
Dim submenu_dropdownindex As Integer = mainmenu.DropDownItems.IndexOf(submenu)
 
If mainmenu_itemindex < 0 Then
   MsgBox("Mainmenu nicht im Menustrip enthalten")
Else
   MsgBox("Mainmenu im Menustrip enthalten: " & CStr(mainmenu_itemindex))
 
   If submenu_dropdownindex < 0 Then
      mainmenu.DropDownItems.Add(submenu)
   Else
      MsgBox("Submenu im Maimenu enthalten: " & CStr(submenu_dropdownindex))
   End If
End If

Dim Plugins As New ToolStripMenuItem
With Plugins
   .Text = "Plugins"
   .Name = "Plugins"
   .DropDownItems.Add("Plugins")
End With

        Dim mainmenu As New ToolStripMenuItem
        With mainmenu
            .Text = "Plugins"
            .Name = "Plugins"
            .DropDownItems.Add("test")
        End With
 
        Dim submenu As New ToolStripMenuItem
        With submenu
            .Text = "test"
            .Name = "test"
        End With
 
        Dim mainmenu_itemindex As Integer = start.MenuStrip1.Items.IndexOf( _
          MainMenu)
        Dim submenu_dropdownindex As Integer = MainMenu.DropDownItems.IndexOf( _
        submenu)
 
        If mainmenu_itemindex < 0 Then
            MsgBox("Mainmenu nicht im Menustrip enthalten")
 
            If submenu_dropdownindex < 0 Then
                mainmenu.DropDownItems.Add(submenu)
            Else
                MsgBox("Submenu im Maimenu enthalten: " & CStr( _
                  submenu_dropdownindex))
            End If
        Else
            MsgBox("Mainmenu im Menustrip enthalten: " & CStr( _
              mainmenu_itemindex))
 
            If submenu_dropdownindex < 0 Then
                MainMenu.DropDownItems.Add(submenu)
            Else
                MsgBox("Submenu im Maimenu enthalten: " & CStr( _
                  submenu_dropdownindex))
            End If
        End If

 
        Dim mainmenu As New ToolStripMenuItem
        start.menustrip1.Items.Add(mainmenu) 'entfällt, falls bereits in 
        ' MenuStrip1 vorhanden
 
        'Referenz auf Mainmenu in "start"/menustrip1 (Annahme .Name= 
        ' "keyofmainmenu")
        Dim MainMenu As ToolStripMenuItem = _
         CType(start.menustrip1.Items(start.menustrip1.Items.IndexOfKey( _
         "keyofmainmenu")), ToolStripMenuItem)
 
        With mainmenu
            .Text = "Plugins"
            .Name = "Plugins"
            Dim tsi As ToolStripMenuItem = CType(.DropDownItems.Add("test"), _
              ToolStripMenuItem)
            tsi.Name = "keyoftest" 'Schlüssel setzen, nachdem Objektreferenz 
            ' besorgt 
        End With
 
        Dim submenu As New ToolStripMenuItem
        With submenu
            .Text = "test"
            .Name = "keyoftest"
        End With
 
        Dim mainmenu_itemindex As Integer = MenuStrip1.Items.IndexOf( _
          mainmenu)
        'Schlüssel prüfen 
        Dim submenu_dropdownindex As Integer = _
          mainmenu.DropDownItems.IndexOfKey("keyoftest")
 
        If mainmenu_itemindex < 0 Then
            MsgBox("Mainmenu nicht im Menustrip enthalten")
 
            If submenu_dropdownindex < 0 Then
                mainmenu.DropDownItems.Add(submenu)
            Else
                MsgBox("Submenu im Maimenu enthalten: " & CStr( _
                  submenu_dropdownindex))
            End If
        Else
            MsgBox("Mainmenu im Menustrip enthalten: " & CStr( _
              mainmenu_itemindex))
 
            If submenu_dropdownindex < 0 Then
                mainmenu.DropDownItems.Add(submenu)
            Else
                MsgBox("Submenu im Maimenu enthalten: " & CStr( _
                  submenu_dropdownindex))
            End If
        End If
    End Sub

Dim MainMenu As ToolStripMenuItem = _
         CType(start.menustrip1.Items(start.menustrip1.Items.IndexOfKey( _
         "keyofmainmenu")), ToolStripMenuItem)

    Dim MainMenu As ToolStripMenuItem = _
         CType(start.MenuStrip1.Items(start.MenuStrip1.Items.IndexOfKey( _
         "Plugins")), ToolStripMenuItem)

    Private Sub Button1_Click_1(sender As System.Object, e As System.EventArgs) _
      Handles Button1.Click
        Dim menuitems() As String = myplugin.MenuItemTexte
 
        'Dim mainmenu As New ToolStripMenuItem
        'start.MenuStrip1.Items.Add(mainmenu) 'entfällt, falls bereits in
 
        ' MenuStrip1 vorhanden
        'Referenz auf Mainmenu in "start"/menustrip1 (Annahme .Name= 
        ' "keyofmainmenu")
        Dim MainMenu As ToolStripMenuItem = _
         CType(start.MenuStrip1.Items(start.MenuStrip1.Items.IndexOfKey( _
         "Plugins")), ToolStripMenuItem)
 
        With mainmenu
            .Text = "Plugins"
            .Name = "Plugins"
            Dim tsi As ToolStripMenuItem = CType(.DropDownItems.Add("test"),  _
              ToolStripMenuItem)
            tsi.Name = "keyoftest" 'Schlüssel setzen, nachdem Objektreferenz 
            ' besorgt 
        End With
 
        Dim submenu As New ToolStripMenuItem
        With submenu
            .Text = "test"
            .Name = "keyoftest"
        End With
 
        Dim mainmenu_itemindex As Integer = start.MenuStrip1.Items.IndexOf( _
          MainMenu)
        'Schlüssel prüfen 
        Dim submenu_dropdownindex As Integer = _
          MainMenu.DropDownItems.IndexOfKey("keyoftest")     ' < 
          ' ========================== INDEXOFKEY wie du geschrieben hast
 
        If mainmenu_itemindex < 0 Then
            MsgBox("Mainmenu nicht im Menustrip enthalten")
 
            If submenu_dropdownindex < 0 Then
                mainmenu.DropDownItems.Add(submenu)
            Else
                MsgBox("Submenu im Maimenu enthalten: " & CStr( _
                  submenu_dropdownindex))
            End If
        Else
            MsgBox("Mainmenu im Menustrip enthalten: " & CStr( _
              mainmenu_itemindex))
 
            If submenu_dropdownindex < 0 Then
                mainmenu.DropDownItems.Add(submenu)
            Else
                MsgBox("Submenu im Maimenu enthalten: " & CStr( _
                  submenu_dropdownindex))
            End If
        End If
    End Sub

        'Dim mainmenu As New ToolStripMenuItem
        'start.MenuStrip1.Items.Add(mainmenu) 'entfällt, falls bereits in
 
        ' MenuStrip1 vorhanden
        'Referenz auf Mainmenu in "start"/menustrip1 (Annahme .Name= 
        ' "keyofmainmenu")
        Dim MainMenu As ToolStripMenuItem = _
         CType(start.MenuStrip1.Items(start.MenuStrip1.Items.IndexOfKey( _
         "Plugins")), ToolStripMenuItem)
 
        With mainmenu
            .Text = "Plugins"
            .Name = "Plugins"
            'Dim tsi As ToolStripMenuItem = CType(.DropDownItems.Add("test"),  _
            'ToolStripMenuItem)
            'tsi.Name = "keyoftest" 'Schlüssel setzen, nachdem Objektreferenz 
            ' besorgt 
        End With
 
        Dim submenu As New ToolStripMenuItem
        With submenu
            .Text = "test"
            .Name = "keyoftest"
        End With
 
        Dim mainmenu_itemindex As Integer = start.MenuStrip1.Items.IndexOf( _
          MainMenu)
        'Schlüssel prüfen 
        Dim submenu_dropdownindex As Integer = _
          MainMenu.DropDownItems.IndexOfKey("keyoftest")
 
        If mainmenu_itemindex < 0 Then
            MsgBox("Mainmenu nicht im Menustrip enthalten")
 
            If MainMenu.DropDownItems.ContainsKey("keyofsubitem") Then Exit Sub
 
            Dim subitem As New ToolStripMenuItem
            subitem.Text = "Sub Item"
            subitem.Name = "keyofsubitem"
            MainMenu.DropDownItems.Add(subitem)
        Else
            MsgBox("Mainmenu im Menustrip enthalten: " & CStr( _
              mainmenu_itemindex))
 
            If MainMenu.DropDownItems.ContainsKey("keyofsubitem") Then Exit Sub
 
            Dim subitem As New ToolStripMenuItem
            subitem.Text = "Sub Item"
            subitem.Name = "keyofsubitem"
            MainMenu.DropDownItems.Add(subitem)
        End If