在Swift中设置UIButton的Autolayout约束

Question

我仍然试图在XCode 6.3中了解Swift Autolayouts.我已经设置了一个View Controller,我在Interface Builder中粘贴了几个标签.我已经以编程方式添加了UITextView和UIImageView,并且我尝试在屏幕底部添加UIButton并以编程方式设置其约束.但是,当视图尝试加载时,我不断收到错误.

根据类定义:

let infoButton = UIButton.buttonWithType(UIButtonType.System) as! UIButton
var descView: UITextView!
var picView: UIImageView!

override func viewDidLoad() {
  super.viewDidLoad()
  infoButton.setTranslatesAutoresizingMaskIntoConstraints(false)
  infoButton.setTitle("Information",forState:UIControlState.Normal)
  self.view.addSubview(infoButton)

self.descView = UITextView(frame:CGRectMake(0,0,300,290))
self.descView.selectable = false
self.userInteractionEnabled = false
self.descView.text = "testing block of text"

self.container.frame = CGRect(x:20,y:160,width:300,height:290)
self.picView = UIImageView(image:"house.png")
self.view.addSubview(container)
self.container.addSubview(picView)

//setup button constraints
let viewsDictionary = ["infoButton":infoButton]
let button_constraint_H:Array = NSLayoutConstraint.constraintsWithVisualFormat("H:|-[infoButton]-|", options:NSLayoutFormatOptions(0),metrics:nil,views:viewsDictionary)
let button_constraint_V:Array = NSLayoutConstraint.constraintsWithVisualFormat("V:[infoButton]-0-|",options:NSLayoutFormatOptions(0),metrics:nil, views:viewsDictionary)
infoButton.addConstraints(button_constraint_H)
infoButton.addConstraints(button_constraint_V)

}

该应用程序在viewDidLoad()方法中崩溃.

2015-06-17 16:59:14.902 LayoutTest[20323:5937743] The view hierarchy is not prepared for the constraint: <NSLayoutConstraint:0x7fc5b9de4140 UIButton:0x7fc5b9ec3e40'Information'.leading == UIView:0x7fc5b9eaf860.leadingMargin>
When added to a view, the constraint's items must be descendants of that view (or the view itself). This will crash if the constraint needs to be resolved before the view hierarchy is assembled. Break on -[UIView _viewHierarchyUnpreparedForConstraint:] to debug.
2015-06-17 16:59:14.904 LayoutTest[20323:5937743] View hierarchy unprepared for constraint.
Constraint: <NSLayoutConstraint:0x7fc5b9de4140 UIButton:0x7fc5b9ec3e40'Information'.leading == UIView:0x7fc5b9eaf860.leadingMargin>
Container hierarchy: 
<UIButton: 0x7fc5b9ec3e40; frame = (0 0; 0 0); opaque = NO; layer = <CALayer: 0x7fc5b9ee2a80>>
View not found in container hierarchy: <UIView: 0x7fc5b9eaf860; frame = (0 0; 375 667); autoresize = W+H; layer = <CALayer: 0x7fc5b9ed9c70>>
That view's superview: NO SUPERVIEW
2015-06-17 16:59:14.925 LayoutTest[20323:5937743] *** Terminating app due to uncaught exception 'NSGenericException', reason: 'Unable to install constraint on view.  Does the constraint reference something from outside the subtree of the view?  That's illegal. constraint:<NSLayoutConstraint:0x7fc5b9de4140 UIButton:0x7fc5b9ec3e40'Information'.leading == UIView:0x7fc5b9eaf860.leadingMargin> view:<UIButton: 0x7fc5b9ec3e40; frame = (0 0; 0 0); opaque = NO; layer = <CALayer: 0x7fc5b9ee2a80>>'

我究竟做错了什么？
我已经使用Interface Builder为其他项(标签)定义了一些约束,但需要能够定义按钮等,并通过代码为同一视图设置约束.

这是我与Swift的第一周,所以要温柔!斤

Answer 1

试试这段代码

        self.view.addConstraint(NSLayoutConstraint(item: infoButton, attribute: NSLayoutAttribute.Leading, relatedBy: NSLayoutRelation.Equal, toItem: self.view, attribute: NSLayoutAttribute.Leading, multiplier: 1.0, constant: 0.0))
        self.view.addConstraint(NSLayoutConstraint(item: infoButton, attribute: NSLayoutAttribute.Trailing, relatedBy: NSLayoutRelation.Equal, toItem: self, attribute: NSLayoutAttribute.Trailing, multiplier: 1.0, constant: 0.0))
        self.view.addConstraint(NSLayoutConstraint(item: infoButton, attribute: NSLayoutAttribute.Bottom, relatedBy: NSLayoutRelation.Equal, toItem: self.view, attribute: NSLayoutAttribute.Bottom, multiplier: 1.0, constant: 0.0))