Swift如何在没有设置框架的情况下获得frame.width？

Question

我有这个文本域

let usn_text_field: LeftPaddedTextField = {
        let tf = LeftPaddedTextField()
        tf.placeholder = "Username"
        tf.translatesAutoresizingMaskIntoConstraints = false
        return tf
    }()
    usn_text_field.topAnchor.constraint(equalTo: info_centill.bottomAnchor).isActive = true
    usn_text_field.leftAnchor.constraint(equalTo: view.leftAnchor,constant:20).isActive = true
    usn_text_field.rightAnchor.constraint(equalTo: view.rightAnchor,constant:-75).isActive = true

我想为此tf添加边框图层，她是我的代码

let borderLayer = CALayer()
    borderLayer.frame = CGRect(x:-5,y:39,width:usn_text_field.frame.width,height:1)
    borderLayer.backgroundColor = UIColor(white: 0.7, alpha: 0.6).cgColor
    usn_text_field.layer.addSublayer(borderLayer)

但是这会将usn_text_field.frame.width返回为0.如果没有设置宽度，我可以获得frame.width，还是有其他方法可以获得元素的宽度？

Answer 1

添加layoutIfNeeded为我工作