无法在只有一个约束是通过视觉格式语言设置为同时满足约束条件

Question

我做了一个新的项目，以实践的iOS自动版式功能，视觉格式语言

我只取得了一个按钮，如下

var button:UIButton! 

我做了一个方法，这将增加按钮self.view，命名initViews如下

func initViews() -> Void { 

     button = UIButton() 
     button.setTitle("Button", forState: .Normal) 
     button.backgroundColor = UIColor.blueColor() 

     self.view.addSubview(button) 
     self.createConstraints() 
    } 

这之后我创建了另一个方法，如下面的设置约束。

func createConstraints() -> Void { 

    //Views to add constraints to 
    let views = Dictionary(dictionaryLiteral: ("button",button)) 

    let horizontalConstraints = NSLayoutConstraint.constraintsWithVisualFormat("H:|-[button]-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views) 
    self.view.addConstraints(horizontalConstraints) 

//  let verticalConstraints = NSLayoutConstraint.constraintsWithVisualFormat("V:|-[button]-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views) 

    //self.view.addConstraints(verticalConstraints) 
} 

现在，我打电话viewDidLoad中initViews，但因为它执行，它给在日志警告。

我相信我不能看到没有垂直约束的按钮。但我更关注警告。

警告：

2015-07-12 11:10:06.495 iOSAdvanceAutoLayout Project[1248:37226] 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) 
(
    "<NSLayoutConstraint:0x7fc9f062ffb0 UIButton:0x7fc9f061ccd0'Button'.leading == UIView:0x7fc9f0572cb0.leadingMargin>", 
    "<NSLayoutConstraint:0x7fc9f0630180 UIView:0x7fc9f0572cb0.trailingMargin == UIButton:0x7fc9f061ccd0'Button'.trailing>", 
    "<NSAutoresizingMaskLayoutConstraint:0x7fc9f056a820 h=--& v=--& H:[UIButton:0x7fc9f061ccd0'Button'(0)]>", 
    "<NSLayoutConstraint:0x7fc9f056d0e0 'UIView-Encapsulated-Layout-Width' H:[UIView:0x7fc9f0572cb0(375)]>" 
) 

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7fc9f0630180 UIView:0x7fc9f0572cb0.trailingMargin == UIButton:0x7fc9f061ccd0'Button'.trailing> 

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. 
2015-07-12 11:10:06.496 iOSAdvanceAutoLayout Project[1248:37226] 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) 
(
    "<NSLayoutConstraint:0x7fc9f062ffb0 UIButton:0x7fc9f061ccd0'Button'.leading == UIView:0x7fc9f0572cb0.leadingMargin>", 
    "<NSAutoresizingMaskLayoutConstraint:0x7fc9f056c210 h=--& v=--& UIButton:0x7fc9f061ccd0'Button'.midX ==>", 
    "<NSAutoresizingMaskLayoutConstraint:0x7fc9f056a820 h=--& v=--& H:[UIButton:0x7fc9f061ccd0'Button'(0)]>", 
    "<NSAutoresizingMaskLayoutConstraint:0x7fc9f056d880 h=-&- v=-&- 'UIView-Encapsulated-Layout-Left' H:|-(0)-[UIView:0x7fc9f0572cb0] (Names: '|':UIWindow:0x7fc9f061b9d0)>" 
) 

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7fc9f062ffb0 UIButton:0x7fc9f061ccd0'Button'.leading == UIView:0x7fc9f0572cb0.leadingMargin> 

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. 

任何人都可以指导我，为什么这个警告是有，而只有一个约束条件设置？
感谢

Answer 1

添加以下行创建按钮

button.translatesAutoresizingMaskIntoConstraints = false 

同时添加的垂直约束，编辑方法如下之后。

func createConstraints() -> Void { 

     //Views to add constraints to 
     let views = Dictionary(dictionaryLiteral: ("button",button)) 

     let horizontalConstraints = NSLayoutConstraint.constraintsWithVisualFormat("H:|-30.0-[button]-30.0-|", 
            options: NSLayoutFormatOptions(rawValue: 0), 
            metrics: nil, 
            views: views) 
     self.view.addConstraints(horizontalConstraints) 



     let verticalConstraints = NSLayoutConstraint.constraintsWithVisualFormat("V:|-30.0-[button]-30.0-|", 
            options: NSLayoutFormatOptions(rawValue: 0), 
            metrics: nil, 
            views: views) 

     self.view.addConstraints(verticalConstraints) 
    }