swift - 以编程方式使用自动布局在 UIVIew 中将 UITextField 设置为中心

Question

我有一个 TextField，必须设置在 UIView 的中心
这是约束

var dict = ["txtHome" : txtHome]
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-[txtHome]-|", options: nil, metrics: nil, views: dict))
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-(>=90,<=100)-[txtHome(20)]-|", options: nil, metrics: nil, views: dict))

但是我得到了日志，

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) 
(
    "<NSLayoutConstraint:0x7966d210 V:|-(<=100)-[UITextField:0x79666440]   (Names: '|':UIView:0x796637d0 )>",
    "<NSLayoutConstraint:0x7966d280 V:[UITextField:0x79666440(20)]>",
    "<NSLayoutConstraint:0x7966d240 UIView:0x796637d0.bottomMargin == UITextField:0x79666440.bottom>",
    "<NSLayoutConstraint:0x7966e880 'UIView-Encapsulated-Layout-Height' V:[UIView:0x796637d0(480)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7966d240 UIView:0x796637d0.bottomMargin == UITextField:0x79666440.bottom>

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.

我不明白他试图告诉我什么来帮助我摆脱困境。

Answer 1

要删除输出，只需添加txtHome.setTranslatesAutoresizingMaskIntoConstraints(false)

在没有约束的情况下， View 使用自动调整大小掩码进行布局 UIView reference , guide