标签约束无效

Question

class videoCell:UICollectionViewCell
{
    override init(frame: CGRect) {
    super.init(frame: frame)
        setUpViews()

    }
   let titlelabel : UILabel =
        {
            var label = UILabel()
        label.backgroundColor = UIColor.brown
        label.translatesAutoresizingMaskIntoConstraints = false
            return label
        }()

    func setUpViews()
    {

        addSubview(titlelabel)

        addConstraint(NSLayoutConstraint(item: titlelabel, attribute:.top, relatedBy: .equal, toItem: thumbNailImageView, attribute: .bottom, multiplier: 1, constant: 8))
        addConstraint(NSLayoutConstraint(item: titlelabel, attribute:.left, relatedBy: .equal, toItem: thumbNailImageView, attribute: .right, multiplier: 1, constant: 8))
        addConstraint(NSLayoutConstraint(item: titlelabel, attribute: .right, relatedBy: .equal, toItem: thumbNailImageView, attribute: .right, multiplier: 1, constant: 0))

        addConstraintsWithFormat(format: "V:[v0(20)]", views:titlelabel)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

extension UIView
{

    func addConstraintsWithFormat(format:String,views:UIView...)
    {
        var allViews = [String:UIView]()
        for data in 0...views.count-1
        {
            let key = "v\(data)"
            allViews[key] = views[data]
        }
        addConstraints(NSLayoutConstraint.constraints(withVisualFormat: format, options: NSLayoutFormatOptions(), metrics: nil, views: allViews))

    }


}

我的上述函数setUpViews()没有在view.Can上呈现我的标签--任何人都可以在这里帮助我。我没有收到任何错误，它编译很好，但没有输出。

addConstraints方法有什么问题吗？

请帮忙谢谢。

如果我添加了这个约束-：

addConstraintsWithFormat(format: "H:|[v0]|", views:titlelabel)

并注释这一行代码-：

addConstraint(NSLayoutConstraint(item: titlelabel, attribute:.left, relatedBy: .equal, toItem: thumbNailImageView, attribute: .right, multiplier: 1, constant: 8))
        addConstraint(NSLayoutConstraint(item: titlelabel, attribute: .right, relatedBy: .equal, toItem: thumbNailImageView, attribute: .right, multiplier: 1, constant: 0))

但这并不能表明我的观点，我需要的地方，以及我希望它如何发挥作用。

Answer 1

好，就这样解决了-：

addConstraint(NSLayoutConstraint(item: titlelabel, attribute: .top, relatedBy: .equal, toItem: thumbNailImageView, attribute: .bottom, multiplier: 1.0, constant: 8))
        addConstraint(NSLayoutConstraint(item: titlelabel, attribute: .leading, relatedBy: .equal, toItem: thumbNailImageView, attribute: .leading, multiplier: 4.0, constant: 8))
        addConstraint(NSLayoutConstraint(item: titlelabel, attribute: .trailing, relatedBy: .equal, toItem: thumbNailImageView, attribute: .trailing, multiplier: 1.0, constant: 0))
        addConstraint(NSLayoutConstraint(item: titlelabel, attribute: .height, relatedBy: .equal, toItem: self, attribute: .height, multiplier: 0, constant: 20))

但谁能详细解释一下这是怎么回事。这是谷歌搜索出的答案。

Answer 2

您必须在setUpViews()方法中调用您的awakeFromNib()函数。