Question

我第一次使用代码设置AutoLayout视图的约束（我需要在不同的viewControllers中创建动态视图，我更喜欢在运行中创建这个UIView＆＃34;）。 / p>

我的UIView应附加到superview top，与superview一样大，底部应附加到特定视图（导航栏）的顶部。

我尝试了以下内容：

let newView = UIView()
newView.backgroundColor = UIColor.red
view.addSubview(newView)

newView.translatesAutoresizingMaskIntoConstraints = false

let verticalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0)

let widthConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: view,attribute: NSLayoutAttribute.width, multiplier: 1, constant: 0)

let bottomConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.bottom, relatedBy: NSLayoutRelation.equal, toItem: navigationBar, attribute: NSLayoutAttribute.top, multiplier: 1, constant: 0)

NSLayoutConstraint.activate([verticalConstraint, widthConstraint, bottomConstraint])

我收到以下运行时错误，但我无法理解什么是无用的约束：我有一个手动创建的视图具有相同的约束（还有一个更多）和我没有错误：

[LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x60800009d060 UINavigationBar:0x7f8061c0d2b0.top == UILayoutGuide:0x6080001ace80'UIViewSafeAreaLayoutGuide'.top   (active)>",
    "<NSLayoutConstraint:0x60400008fc80 UIView:0x7f8061f13b20.centerY == UIView:0x7f8061c17ce0.centerY   (active)>",
    "<NSLayoutConstraint:0x60400008faa0 UIView:0x7f8061f13b20.bottom == UINavigationBar:0x7f8061c0d2b0.top   (active)>",
    "<NSLayoutConstraint:0x60000009b120 'UIView-Encapsulated-Layout-Height' UIView:0x7f8061c17ce0.height == 667   (active)>",
    "<NSLayoutConstraint:0x60800009d0b0 'UIViewSafeAreaLayoutGuide-top' V:|-(20)-[UILayoutGuide:0x6080001ace80'UIViewSafeAreaLayoutGuide']   (active, names: '|':UIView:0x7f8061c17ce0 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x60400008fc80 UIView:0x7f8061f13b20.centerY == UIView:0x7f8061c17ce0.centerY   (active)>

感谢任何帮助

Answer 1

只需在自定义视图的超级视图中添加顶部，前导，尾随约束。将底部约束添加到顶部另一个视图，该视图将位于自定义视图＆amp;也是自定义视图的超级视图的子视图。

在您的代码中，问题也在于您的底部约束。您正尝试在自定义视图的底部添加约束b / w;导航栏顶部。

 let topConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.top, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.top, multiplier: 1, constant: 0)

let leadingConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.leading, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.leading, multiplier: 1, constant: 0)

let trailingConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.trailing, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.trailing, multiplier: 1, constant: 0)

let bottomConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.bottom, relatedBy: NSLayoutRelation.equal, toItem: anotherView, attribute: NSLayoutAttribute.top, multiplier: 1, constant: 0)

Answer 2

您不需要对centerY属性使用约束。由于您的目标是将视图固定到顶部，请尝试使用topAnchor约束并使其等于superview.topAnchor。希望这会有所帮助：

let newView = UIView()
newView.backgroundColor = UIColor.red
view.addSubview(newView)

newView.translatesAutoresizingMaskIntoConstraints = false

let topConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.topAnchor, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.topAnchor, multiplier: 1, constant: 0)

let widthConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: view,attribute: NSLayoutAttribute.width, multiplier: 1, constant: 0)

let bottomConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.bottom, relatedBy: NSLayoutRelation.equal, toItem: navigationBar, attribute: NSLayoutAttribute.top, multiplier: 1, constant: 0)

NSLayoutConstraint.activate([verticalConstraint, widthConstraint, bottomConstraint])

设置自动布局约束会导致无法同时满足约束条件＆＃39;错误

2 个答案: