更改UISearchBar TextField的大小？

func updateSearchBarTextFieldSize(searchBar: UISearchBar) {
    for subview in searchBar.subviews {
        for subsubview in subview.subviews {
            if let textField = subsubview as? UITextField {
                let widthConstraint = NSLayoutConstraint(item: textField, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 200)
                let heightConstraint = NSLayoutConstraint(item: textField, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 40)
                textField.addConstraints([widthConstraint, heightConstraint])
            }
        }
    }
}