有没有一种方法，以一个标识符在Interface Builder添加到自动布局限制？ [英] Is there a way to add an identifier to Auto Layout Constraints in Interface Builder?

问题描述

在Interface Builder做一些视觉上的布局后，我创造了一些限制，我想在运行时访问。有没有一种方法来标记或在Interface Builder找出制约，使他们能够看行动以后呢？

After doing some visual layout in Interface Builder I've created some constraints that I want to access at runtime. Is there a way to label or identify constraints in Interface Builder so they can be looked-up later?

我想这样做的原因是，我需要对那些在视觉上指定的约束执行一些计算基数。我知道，苹果提供了<一个href=\"https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/AutolayoutPG/VisualFormatLanguage/VisualFormatLanguage.html#//apple_ref/doc/uid/TP40010853-CH3-SW1\">Visual格式语言，我可以在控制器编程方式指定的约束。我宁可不使用这种方法，所以我不会失去IB的设计时间反馈。

The reason I want to do this is I need to perform some calculation base upon the constraints that are visually specified. I am aware that Apple has provided the Visual Format Language and I could specify the constraints programmatically in a controller. I rather not use this approach so I don't lose the design time feedback of IB.

将参照插座没有工作，但问题仍然有效。

Making a referencing outlet did work, but the question still stands.

推荐答案

是的，这是可以做到。 NSLayoutConstraint 有一个名为属性标识符，无法在界面生成器的暴露和分配。为了演示这一点，我创建了一个的单查看应用程序的，有一个单独的子视图是一个红色的盒子。此子视图有4个限制：宽度，高度，水平在容器中心，集装箱垂直居中。我给宽度约束标识符 redBoxWidth 通过执行以下操作：

Yes, this can be done. NSLayoutConstraint has a property called identifier than can be exposed in Interface Builder and assigned. To demo this, I created a Single View Application that has a single subview that is a red box. This subview has 4 constraints: width, height, centered horizontally in container, centered vertically in container. I gave the width constraint the identifier redBoxWidth by doing the following:

1. 在文档版式视图点击宽度约束的。然后在身份检查的在用户定义运行属性，点击 + 在键路径。变化的的keyPath 的到的标识的，改变的类型 布尔的到的字符串的，并设置值以 redBoxWidth 。

1. Click on the width constraint in the Document Layout View. Then in the Identity Inspector under User Defined Runtime Attributes, click on the + under Key Path. Change keyPath to identifier, change the Type Boolean to String, and set the Value to redBoxWidth.

然后在 viewDidLoad中可以通过名字来查找约束并改变它的值：

Then in ViewDidLoad it is possible to find the constraint by name and change its value:

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        for subview in view.subviews as [UIView] {
            for constraint in subview.constraints() as [NSLayoutConstraint] {
                if constraint.identifier == "redBoxWidth" {
                    constraint.constant = 300
                }
            }
        }
    }
}

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