UIButton角半径在CustomClass中无法正常工作

设置cornerRadiusin awakeFromNib为时过早。使用layoutSubviews来代替：

class CustomRoundButton: UIButton {

    override func awakeFromNib() {
        super.awakeFromNib()
        layer.borderColor = UIColor.blue.cgColor
        layer.borderWidth = 1
    }

    override func layoutSubviews() {
        super.layoutSubviews()
        layer.cornerRadius = layer.frame.height / 2
    }

}