编程约束 - 使用布局锚覆盖整个超级视图答案

【问题标题】：programmatic constraints - cover entire superview using layout anchors编程约束 - 使用布局锚覆盖整个超级视图
【发布时间】：2016-10-28 08:37:47
【问题描述】：

是否可以使用布局锚点覆盖整个超级视图的屏幕？

使用NSLayoutConstraints，我可以使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

我想改用布局锚点，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

但两者都不起作用。我最终得到的不是完全覆盖容器视图，而是所有 4 个边的填充。

【问题讨论】：

标签： ios swift nslayoutconstraint nslayoutanchor

【解决方案1】：

您正在限制边距，边距是您看到的空间。改为使用 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

【讨论】：

【解决方案2】：

您必须使用属性.leading、.trailing、.top和.bottom，而不是对应的.xxxMargin属性。他们将沿着 superviews 边界放置子视图。

【讨论】：