Question

我想在collectionView的顶部创建一个粘性标题，所以当我尝试滚动时，标题将始终存在。

以下代码是有效的。

collectionView?.contentInset = UIEdgeInsets(top: 59, left: 0, bottom: 0, right: 0)

if let width = collectionView?.bounds.width {
    let heaaderEffectView = UIVisualEffectView(effect: UIBlurEffect(style: .Light))
    heaaderEffectView.frame = CGRectMake( 0, 64, width, 59)

    let headerView = DetailedReviewsHeader(frame: CGRectMake( 0, 0, width, 59))
    heaaderEffectView.contentView.addSubview(headerView)
    headerView.numberOfReviews = reviews?.count ?? 0
    headerView.sortButton.addTarget(self, action: #selector(showSortOptions(_:)), forControlEvents: .TouchUpInside)

    view.addSubview(heaaderEffectView)
}

我想如何将此行替换为autolayout

heaaderEffectView.frame = CGRectMake( 0, 64, width, 59)

我试过了

  view.addSubview(headerEffectView)
  headerEffectView.topAnchor.constraintEqualToAnchor(view.topAnchor).active = true
  headerEffectView.heightAnchor.constraintEqualToConstant(59.0).active = true

但它不起作用。帧总是（0,0,0,0）。有什么想法吗？

Answer 1

我添加了应用约束的代码。这是您的要求的代码。尝试一次。仔细查看行尾的注释。

collectionView?.contentInset = UIEdgeInsets(top: 59, left: 0, bottom: 0, right: 0)

if let width = collectionView?.bounds.width {
    let heaaderEffectView = UIVisualEffectView(effect: UIBlurEffect(style: .Light))
    //heaaderEffectView.frame = CGRectMake( 0, 64, width, 59)

    view.addSubview(heaaderEffectView)
    heaaderEffectView.translatesAutoresizingMaskIntoConstraints = false

    heaaderEffectView.addConstraint(NSLayoutConstraint(item: heaaderEffectView, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1.0, constant: width))// for width of heaaderEffectView
    heaaderEffectView.addConstraint(NSLayoutConstraint(item: heaaderEffectView, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1.0, constant: 59.0))// for height of heaaderEffectView
    view.addConstraint(NSLayoutConstraint(item: heaaderEffectView, attribute: NSLayoutAttribute.Top, relatedBy: NSLayoutRelation.Equal, toItem: view, attribute: NSLayoutAttribute.Top, multiplier: 1.0, constant: 64.0))// for y spacing that is top constraint to super view from heaaderEffectView
    view.addConstraint(NSLayoutConstraint(item: heaaderEffectView, attribute: NSLayoutAttribute.Bottom, relatedBy: NSLayoutRelation.Equal, toItem: view, attribute: NSLayoutAttribute.Bottom, multiplier: 1.0, constant: 0.0))// for x spacing that is leading constraint to super view from heaaderEffectView

    let headerView = DetailedReviewsHeader(frame: CGRectMake( 0, 0, width, 59))// you can remove using frame but i kept it because i don't know what the initializer does with the frame
    headerView.numberOfReviews = reviews?.count ?? 0
    headerView.sortButton.addTarget(self, action: #selector(showSortOptions(_:)), forControlEvents: .TouchUpInside)

    heaaderEffectView.contentView.addSubview(headerView)
    headerView.translatesAutoresizingMaskIntoConstraints = false

    heaaderEffectView.addConstraint(NSLayoutConstraint(item: headerView, attribute: NSLayoutAttribute.Leading, relatedBy: NSLayoutRelation.Equal, toItem: heaaderEffectView, attribute: NSLayoutAttribute.Leading, multiplier: 1.0, constant: 0.0))// for leading 0
    heaaderEffectView.addConstraint(NSLayoutConstraint(item: headerView, attribute: NSLayoutAttribute.Trailing, relatedBy: NSLayoutRelation.Equal, toItem: heaaderEffectView, attribute: NSLayoutAttribute.Trailing, multiplier: 1.0, constant: 0.0))// for trailing 0
    heaaderEffectView.addConstraint(NSLayoutConstraint(item: headerView, attribute: NSLayoutAttribute.Top, relatedBy: NSLayoutRelation.Equal, toItem: heaaderEffectView, attribute: NSLayoutAttribute.Top, multiplier: 1.0, constant: 0.0))// for top 0
    heaaderEffectView.addConstraint(NSLayoutConstraint(item: headerView, attribute: NSLayoutAttribute.Bottom, relatedBy: NSLayoutRelation.Equal, toItem: heaaderEffectView, attribute: NSLayoutAttribute.Bottom, multiplier: 1.0, constant: 0.0))// for bottom 0

    view.layoutIfNeeded()
}

如何使用自动布局约束而不是框架？

1 个答案: