ios 以编程方式快速添加约束
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add constraints programmatically swift
提问by user2363025
I am trying to add constraints to a facebook sdk login button.
我正在尝试向 facebook sdk 登录按钮添加约束。
I have the button inside a scroll view and I am trying to add a top constraint to a label that is also in the scroll view. I am able to successfully add the height constraint with no run time errors but the actual constraint does not seem to be applied to the button.
我在滚动视图中有按钮，我试图向也在滚动视图中的标签添加顶部约束。我能够在没有运行时错误的情况下成功添加高度约束，但实际约束似乎并未应用于按钮。
@IBOutlet weak var orLbl: UILabel!
@IBOutlet weak var scrollView: UIScrollView!
override func viewDidLoad() {
super.viewDidLoad()
var loginFBButton = FBSDKLoginButton()
loginFBButton.readPermissions = ["public_profile", "email"]
let heightConstraint = NSLayoutConstraint(
item: loginFBButton,
attribute: NSLayoutAttribute.Height,
relatedBy: NSLayoutRelation.Equal,
toItem: nil,
attribute: NSLayoutAttribute.NotAnAttribute,
multiplier: 1,
constant: 41)
let topConstraint = NSLayoutConstraint(
item: loginFBButton,
attribute: NSLayoutAttribute.TopMargin,
relatedBy: NSLayoutRelation.Equal,
toItem: self.orLbl,
attribute: NSLayoutAttribute.BottomMargin,
multiplier: 1,
constant: 31)
let leadingConstraint = NSLayoutConstraint(
item: loginFBButton,
attribute: NSLayoutAttribute.Leading,
relatedBy: NSLayoutRelation.Equal,
toItem: self.registerButton,
attribute: NSLayoutAttribute.Left,
multiplier: 1,
constant: 0)
let trailingConstraint = NSLayoutConstraint(
item: loginFBButton,
attribute: NSLayoutAttribute.Leading,
relatedBy: NSLayoutRelation.Equal,
toItem: self.registerButton,
attribute: NSLayoutAttribute.Right,
multiplier: 1,
constant: 0)
self.scrollView.addSubview(loginFBButton)
//loginFBButton.center = self.scrollView.center
loginFBButton.addConstraints([heightConstraint, topConstraint])
}
Then when I include the addition of the top constraint, I am getting a runtime error:
然后，当我添加顶部约束时，出现运行时错误：
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.
添加到视图时，约束的项必须是该视图（或视图本身）的后代。如果在组装视图层次结构之前需要解决约束，这将崩溃。
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.
由于未捕获的异常“NSGenericException”而终止应用程序，原因：“无法在视图上安装约束。约束是否引用了视图子树之外的内容？那是非法的。
Both the label and the facebook button are in my scroll view? I've even printed out orLbl.superview and loginFBButton.superview and I am getting optional uiscrollview for both
标签和 facebook 按钮都在我的滚动视图中？我什至打印了 orLbl.superview 和 loginFBButton.superview 并且我都得到了可选的 uiscrollview
回答by vacawama
There is a new (iOS8, OS 10.10), easier way to activate constraints that doesn't involve figuring out which views to add them to. The constraints already know which views they belong to, so first make sure your views have been added as subViews, then call the class method activateConstraintson NSLayoutConstraintto activate them:
有一种新的（iOS8，OS 10.10）更简单的方法来激活约束，而无需弄清楚要将它们添加到哪些视图。约束已经知道哪些意见，他们属于，所以首先要确保你的观点已经被添加为子视图，然后调用类的方法activateConstraints上NSLayoutConstraint激活它们：
NSLayoutConstraint.activateConstraints([heightConstraint, topConstraint])
When you create UI elements programmatically, you need to tell iOS not to turn its frame into constraints. To do that, just after creating loginFBButtondo:
当您以编程方式创建 UI 元素时，您需要告诉 iOS 不要将其框架变成约束。要做到这一点，就在创建之后loginFBButton：
For Swift 1.2:
对于 Swift 1.2：
loginFBButton.setTranslatesAutoresizingMaskIntoConstraints(false)
For Swift 2.0 & 3.0:
对于 Swift 2.0 和 3.0：
loginFBButton.translatesAutoresizingMaskIntoConstraints = false
Finally, you are going to need more constraints. I suggest setting a width constraint for your loginFBButtonand adding a constraint to position the button horizontally.
最后，您将需要更多约束。我建议为您设置一个宽度约束loginFBButton并添加一个约束来水平定位按钮。
