swift - 在 Swift 中子类化 NSLayoutConstraint

Question

我想在 Swift 中子类化 NSLayoutConstraint 以提供更简单的方法来实例化常见约束(例如 height、width ...) .

到目前为止，我编写的代码草稿无法正常工作，因为无法写入 item-properties:

class TestConstraint: NSLayoutConstraint {
    init(item: Any) {
        super.init()
        self.firstItem = item // WARNING: Cannot assign to property: 'firstItem' is a get-only property

        // ...
    }
}

是否有可能以这种方式子类化 NSLayoutConstraint 还是我必须额外考虑其他因素？

Answer 1

我认为您需要的是 UIView 的扩展。

extension UIView{
    func anchor(top:NSLayoutYAxisAnchor?,leading:NSLayoutXAxisAnchor?,trailing:NSLayoutXAxisAnchor?,bottom:NSLayoutYAxisAnchor?,padding:UIEdgeInsets = .zero,size:CGSize = .zero){

        translatesAutoresizingMaskIntoConstraints = false

        if let top = top{
            topAnchor.constraint(equalTo: top, constant: padding.top).isActive = true
        }
        if let leading = leading{
            leadingAnchor.constraint(equalTo: leading, constant: padding.left).isActive = true
        }
        if let trailing = trailing{
            trailingAnchor.constraint(equalTo: trailing, constant: -padding.right).isActive = true
        }
        if let bottom = bottom{
            bottomAnchor.constraint(equalTo: bottom, constant: -padding.bottom).isActive = true
        }
        if size.width != 0{
            widthAnchor.constraint(equalToConstant: size.width).isActive = true
        }
        if size.height != 0{
            heightAnchor.constraint(equalToConstant: size.height).isActive = true
        }
    }

}