ios - 无法在 UICollectionView 单元格和单元格 subview 之间添加约束

Question

在我运行我的应用程序后，它崩溃了:

Unable to install constraint on view. Does the constraint reference something from outside the subtree of the view? That's illegal.

我的图像是单元格的 subview 。

我做错了什么？

let image = UIImageView(frame: CGRect(x: 0, y: 0, width: 300, height: 50))
image.image = UIImage.init(named: "Bitmap")

cell.contentView.addSubview(image)

let bottomConstr = NSLayoutConstraint(item: image, attribute: .bottom, relatedBy: .equal, toItem: cell.contentView, attribute: .bottom, multiplier: 1, constant: 0)
//let leftConstr = NSLayoutConstraint(item: image, attribute: .leading, relatedBy: .equal, toItem: cell.contentView, attribute: .leading, multiplier: 1, constant: 0)
//let rightConstr = NSLayoutConstraint(item: image, attribute: .trailing, relatedBy: .equal, toItem: cell.contentView, attribute: .trailing, multiplier: 1, constant: 0)
let heightConstr = NSLayoutConstraint(item: image, attribute: .height, relatedBy: .equal, toItem: nil , attribute: .notAnAttribute, multiplier: 1, constant: 10)

image.addConstraint(bottomConstr)
//image.addConstraint(leftConstr)
//image.addConstraint(rightConstr)
image.addConstraint(heightConstr)

Answer 1

您需要在 Superview 上添加约束。所以，将它添加到单元格 contentView 上。

  cell.contentView.addConstraint(bottomConstr)
  cell.contentView.addConstraint(heightConstr)