ios - NSLayoutConstraint问题

Question

//MARK: NSLayoutConstraints
//trailing
let trailingConstaint = NSLayoutConstraint(item: imageView, attribute: .trailing, relatedBy: .equal, toItem:imageView.superview , attribute: .trailing, multiplier: 1, constant: 0)
trailingConstaint.isActive = true

//leading
let leadingConstraint = NSLayoutConstraint(item: imageView, attribute: .leading, relatedBy: .equal, toItem: imageView.superview, attribute: .leading, multiplier: 1, constant: 0)
leadingConstraint.isActive = true

//top
let topConstraint = NSLayoutConstraint(item: image, attribute: .top, relatedBy: .equal, toItem: imageView.superview, attribute: .top, multiplier: 1, constant: 0)
topConstraint.isActive = true

//bottom
let bottomConstraint = NSLayoutConstraint(item: imageView, attribute: .bottom, relatedBy: .equal, toItem: imageView.superview, attribute: .bottom, multiplier: 1, constant: 0)
bottomConstraint.isActive = true

我想调整图像大小使其适合，以便正确缩放图像 screenshot of ViewController

但是我得到这个错误..

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'NSLayoutConstraint for size {746, 496} orientation 0 scale 1.000000: Constraint items must each be an instance of UIView, or UILayoutGuide.'

Answer 1

//top
let topConstraint = NSLayoutConstraint(item: image, attribute: .top, relatedBy: .equal, toItem: imageView.superview, attribute: .top, multiplier: 1, constant: 0)
topConstraint.isActive = true

您将此约束设置为 image 而不是 imageView。

异常明确指出约束项必须每个都是 UIView 或 UILayoutGuide 的实例。'

所有其他约束都设置在 imageView 和 imageView.superView 之间，因此从逻辑上讲，上述约束也应该使用同一对。

这将处理异常。

//top
let topConstraint = NSLayoutConstraint(item: imageView, attribute: .top, relatedBy: .equal, toItem: imageView.superview, attribute: .top, multiplier: 1, constant: 0)
topConstraint.isActive = true

但是，图像缩放不能通过约束来实现。您必须适本地设置 contentMode 属性。查看 well-explained docs. 中的了解图像的缩放方式部分