以编程方式为UIView的子视图设置自动布局约束

Question

下面我列出了一些代码供您结账.我正在尝试自定义UIView并添加另一个自定义子视图.这个子视图应该以这样的方式约束到父视图,它基本上只是在相同的维度上放置,而父级只是作为包装器.

NSLayoutConstraint到目前为止,我已尝试使用和失败的悲惨.视图从未真正显示出来.我有一个left,right,bottom和top约束,它应与父视图对齐.

第一个问题是,有人请在使用以下方法时解释或纠正我的逻辑.我想到的项目参数是你想为(customViewChild)设置约束的实际视图.该属性是说我希望my的左边缘customViewChild用于此约束.在relatedBy看起来很简单的,虽然我可能是错的,最后的toItem指向自我这是我CustomViewParent这也有一个.left属性地说,我希望我的孩子和家长的左边缘对齐.这个逻辑有缺陷还是我做错了什么？

NSLayoutConstraint(item: customViewChild!, 
            attribute: .left, 
            relatedBy: .equal,
            toItem: self,
            attribute: .left, 
            multiplier: 1.0, 
            constant: 0.0)

我知道下面的例子很容易用IB完成,但我想了解NSLayoutConstraint,所以请提供相关答案.最后,如果有人能够真正纠正这个代码,那么我有一个有效的例子,那将是非常棒的.

class CustomViewParent: UIView {

    var customViewChild: UIView?

    override init(frame: CGRect) {
        super.init(frame: frame)

        setConstraints()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        setConstraints()
    }

    func setConstraints() {
        customViewChild = UIView()

        addSubview(customViewChild!)
        customViewChild?.translatesAutoresizingMaskIntoConstraints = false

        let leftConstraint = NSLayoutConstraint(item: customViewChild!, 
            attribute: .left, 
            relatedBy: .equal,
            toItem: self,
            attribute: .left, 
            multiplier: 1.0, 
            constant: 0.0).isActive = true

        let rightConstraint = NSLayoutConstraint(item: customViewChild!, 
            attribute: .right, 
            relatedBy: .equal,
            toItem: self,
            attribute: .right, 
            multiplier: 1.0, 
            constant: 0.0).isActive = true

        let topConstraint = NSLayoutConstraint(item: customViewChild!, 
            attribute: .top, 
            relatedBy: .equal,
            toItem: self,
            attribute: .top,
            multiplier: 1.0, 
            constant: 0.0).isActive = true

        let bottomConstraint = NSLayoutConstraint(item: customViewChild!, 
            attribute: .bottom, 
            relatedBy: .equal,
            toItem: self,
            attribute: .bottom, 
            multiplier: 1.0, 
            constant: 0.0).isActive = true

        customViewChild.addConstraint([leftConstraint, rightConstraint, topConstraint, bottomConstraint]);
    }

}

Answer 1

您可能会发现这更容易,更易读......

func setConstraints() {

    if customViewChild == nil {
        customViewChild = UIView()

        addSubview(customViewChild!)
        customViewChild?.translatesAutoresizingMaskIntoConstraints = false

        customViewChild?.leftAnchor.constraint(equalTo: self.leftAnchor).isActive = true
        customViewChild?.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
        customViewChild?.rightAnchor.constraint(equalTo: self.rightAnchor).isActive = true
        customViewChild?.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
    }

}