Custom control with fixed height

I need a custom UITextField with some accessory views above and below it.
If I subclass UIView and make it @IBDesignable, when I instantiate my custom control in Interface Builder, I am able to resize it via the size inspector. This is not what I want: I’d like height to be fixed (programmatically computed adding upper UIView height + middle UIView height + lower UIView height).
If I look at Apple’s controls (for instance Progress bar or UITextField), user can’t change their height (height input field is ghosted)
How could I achieve this in my custom control?

Thank you for your help,