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