ios - 编程约束 - 使用布局 anchor 覆盖整个父 View

Question

是否可以使用布局 anchor 来覆盖整个父 View 的屏幕？

使用NSLayoutConstraints，我可以用下面的代码实现这个效果

dimmingView = UIView()
dimmingView.translatesAutoresizingMaskIntoConstraints = false
dimmingView.backgroundColor = UIColor(white: 0.0, alpha: 0.5)

containerView?.addSubview(dimmingView)

NSLayoutConstraint(item: containerView!, attribute: .leadingMargin, relatedBy: .equal, toItem: dimmingView, attribute: .leadingMargin, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: containerView!, attribute: .trailingMargin, relatedBy: .equal, toItem: dimmingView, attribute: .trailingMargin, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: containerView!, attribute: .topMargin, relatedBy: .equal, toItem: dimmingView, attribute: .topMargin, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: containerView!, attribute: .bottomMargin, relatedBy: .equal, toItem: dimmingView, attribute: .bottomMargin, multiplier: 1, constant: 0).isActive = true

我想改为切换到布局 anchor ，遵循 docs 中的建议.我试过这样做:

let margins = containerView?.layoutMarginsGuide

dimmingView.leadingAnchor.constraint(equalTo: margins.leadingAnchor).isActive = true
dimmingView.trailingAnchor.constraint(equalTo: margins.trailingAnchor).isActive = true
dimmingView.topAnchor.constraint(equalTo: margins.topAnchor).isActive = true
dimmingView.bottomAnchor.constraint(equalTo: margins.bottomAnchor).isActive = true

或者这个

let margins = containerView?.layoutMarginsGuide

dimmingView.heightAnchor.constraint(equalTo: margins.heightAnchor).isActive = true
dimmingView.widthAnchor.constraint(equalTo: margins.widthAnchor).isActive = true
dimmingView.centerXAnchor.constraint(equalTo: margins.centerXAnchor).isActive = true
dimmingView.centerYAnchor.constraint(equalTo: margins.centerYAnchor).isActive = true

但两者均无效。我最终得到的不是完全覆盖 containerview，而是在所有 4 个边上填充。

Answer 1

您受限于页边距，页边距就是您看到的空间。改为约束到 superview:.

    dimmingView.heightAnchor.constraint(equalTo: dimmingView.superview!.heightAnchor).isActive = true
    dimmingView.widthAnchor.constraint(equalTo: dimmingView.superview!.widthAnchor).isActive = true
    dimmingView.centerXAnchor.constraint(equalTo: dimmingView.superview!.centerXAnchor).isActive = true
    dimmingView.centerYAnchor.constraint(equalTo: dimmingView.superview!.centerYAnchor).isActive = true