For each ctl As Control In Controls
    If TypeOf ctl Is TextBox Then
        Dim txt As TextBox = CType(ctl, TextBox)
        AddHandler txt.Enter, AddressOf R01DD0_Enter
    End If
Next

Private myTextboxen As TextBox() = New TextBox(29) {}
 
Public Sub New()
    InitializeComponent()
 
    'Textboxen erstellen
    For i As Integer = 0 to myTextboxen.Length - 1
        Dim idx As Integer = i 'für anonyme Funktion
 
        Dim txt As New TextBox()
        myTextboxen(i) = txt
        txt.Size = New Size(100, 25)
        txt.Top = 20 + (i \ 5) * 30
        txt.Left = 20 + (i Mod 5) * 120
        Controls.Add(txt)
 
        'Ereignishandler hinzufügen
        AddHandler txt.Enter, _
            Sub(ByVal sender As Object, ByVal e As System.EventArgs)
                Debug.WriteLine("Enter-Ereignis von Textbox mit Index " & idx)
            End Sub
    Next
End Sub