xib可视化自定义变量

@IBInspectable 让类的支持kvo的属性可以在Xib里面进行设置

@IBDesignable 让xib里面的设置立即可见
范例

@IBDesignable class PanaStackView: UIView {
    @IBInspectable var cornerRa:CGFloat{
        set{
            self.layer.cornerRadius = newValue
        }
        get{
            return self.layer.cornerRadius
        }
    }
}