Private Sub TextBox1_LostFocus(ByVal sender As Object, ByVal e As _
      System.EventArgs) Handles TextBox1.LostFocus
        Dim txtBox As TextBox = DirectCast(sender, TextBox)
        MsgBox(txtBox.Text)
 
        ' Oder direkt
        MsgBox(DirectCast(sender, TextBox).Text)
    End Sub

        Dim datum As Date
        If DateTime.TryParseExact(txtBox.Text.Trim, "dd.MM.yyyy", New _
          Globalization.CultureInfo("de-DE"), _
          Globalization.DateTimeStyles.None, datum) Then
            MsgBox("Gültiges Datum eingegeben: " & datum.Date)
        Else
            MsgBox("Eingegebenes Datum ist ungültig")
            txtBox.Focus()
        End If