以编程方式设置约束导致 Swift 中的冲突

Question

正如我在 this GitHub issue 中发布的那样，我遇到了一些隐藏的约束问题，每当我尝试添加自己的约束时就会引发错误

2016-04-18 19:22:04.270 Metric Time[1519:447809] 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. 
(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"<NSAutoresizingMaskLayoutConstraint:0x15e670e70 h=--& v=--& Metric_Time.View:0x15e692e70.midX == + 115>",
"<NSLayoutConstraint:0x15e5048c0 Metric_Time.View:0x15e692e70.centerX == UIView:0x15e6953e0.centerX>",
"<NSAutoresizingMaskLayoutConstraint:0x15e55fd30 h=-&- v=-&- 'UIView-Encapsulated-Layout-Left' H:|-(0)-[UIView:0x15e6953e0]   (Names: '|':UIWindow:0x15e688ed0 )>",
"<NSLayoutConstraint:0x15e54e750 'UIView-Encapsulated-Layout-Width' H:[UIView:0x15e6953e0(320)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x15e5048c0 Metric_Time.View:0x15e692e70.centerX == UIView:0x15e6953e0.centerX>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.`

我已经尝试寻找可以创建这些约束的位置，但是在我的 ViewController.swift 文件中搜索关键字，例如 constraint、layout .etc只有我写的代码。

如果有人想弄乱它，我的代码都在GitHub 上。

Answer 1

如果要以编程方式添加约束，则需要关闭 translateAutoresizingMaskIntoConstraints。您也没有足够的约束来满足布局引擎。请记住，UIView 没有固有大小，如果您在视图中使用自动布局，则需要使用约束设置所有内容，而不是依赖约束和框架的混合。一种可能的解决方案是添加一些代码，例如：

        self.view.addSubview(clockView)
        clockView.translatesAutoresizingMaskIntoConstraints = false
        clockView.centerYAnchor.constraintEqualToAnchor(self.view.centerYAnchor, constant: 0.0).active = true
        clockView.centerXAnchor.constraintEqualToAnchor(self.view.centerXAnchor, constant: 0.0).active = true
        clockView.widthAnchor.constraintEqualToConstant(230.0).active = true
        clockView.heightAnchor.constraintEqualToConstant(230.0).active = true

但是，这并不是您想要的，因为当它处于横向时，您的时钟会覆盖您的标签。但是你可以通过clockView.centerYAnchor.constraintEqualToAnchor(self.view.centerYAnchor, constant: 0.0).active = true来解决这个问题