I am using a text view as a comment composer.
In the properties inspector I can\'t find anything like a border style property so that I can make use a rounded rect,
One solution is to add a UITextField below the UITextView, make the UITextView background transparent and disable any user interaction on the UITextField. Then in code change the UITextField frame with something like that
self.textField.frame = CGRectInset(self.textView.frame, 0, -2);
You will have exactly the same look as a text field.
And as suggested by Jon, you should put this piece of code inside [UIViewController viewDidLayoutSubviews] on iOS 5.0+.