在代码中为 topLayoutGuide 和 bottomLayoutGuide 创建自动布局约束

问题描述

Apple 的 documentation 在视图和布局指南之一之间创建自动布局约束仅显示使用 VFL.

Apple's documentation on creating Auto Layout constraints between a view and one of the layout guides only shows an example using VFL.

有没有办法以编程方式创建这些约束没有 VFL(使用NSLayoutConstraint的其他API 或类似)?

Is there any way to create these constraints programmatically without VFL (using NSLayoutConstraint's other API or similar)?

(注意:我是专门询问在代码中执行此操作，而不是在 Interface Builder 中.而且我不希望将指南集的计算 length 设置为约束上的静态常量，我想要一个约束，其中对布局指南长度的更改会自动导致受约束的视图调整位置.)

(Note: I'm specifically asking about doing this in code, not in Interface Builder. And I don't want the calculated length of the guide set as a static constant on a constraint, I want a constraint where changes to the layout guide length would automatically cause the constrained view to adjust position.)

推荐答案

对于要在 UIViewController.topLayoutGuide 下方放置 20 点的 UIButton，请创建 NSLayoutConstraint 像这样:

For a UIButton that you want to place 20 points below the UIViewController.topLayoutGuide you create the NSLayoutConstraint like so:

[NSLayoutConstraint constraintWithItem:self.button
                             attribute:NSLayoutAttributeTop
                             relatedBy:NSLayoutRelationEqual
                                toItem:self.topLayoutGuide
                             attribute:NSLayoutAttributeBottom
                            multiplier:1.0
                              constant:20.0];

在 iOS 9 中，您还可以通过这种方式创建 NSLayoutConstraint:

With iOS 9 you can also create the NSLayoutConstraint this way:

[self.button.topAnchor constraintEqualToAnchor:self.topLayoutGuide.bottomAnchor
                                      constant:20.0];

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