通过 Swift 中的代码自动布局适合父级

Question

我有一个视图正在通过代码创建并作为子视图添加到另一个视图。新的超级视图可以随着时间的推移改变它的框架，我希望新创建的子视图相应地改变它的框架。我如何在 Swift 中通过代码使用自动布局来做到这一点？

Answer 1

这是一个例子：

let view = UIView() // existing view

let subview = UIView()
subview.setTranslatesAutoresizingMaskIntoConstraints(false)

view.addSubview(subview)
view.addConstraint(NSLayoutConstraint(item: subview, attribute: .Top, relatedBy: .Equal, toItem: view, attribute: .Top, multiplier: 1.0, constant: 0.0))
view.addConstraint(NSLayoutConstraint(item: subview, attribute: .Leading, relatedBy: .Equal, toItem: view, attribute: .Leading, multiplier: 1.0, constant: 0.0))
view.addConstraint(NSLayoutConstraint(item: view, attribute: .Bottom, relatedBy: .Equal, toItem: subview, attribute: .Bottom, multiplier: 1.0, constant: 0.0))
view.addConstraint(NSLayoutConstraint(item: view, attribute: .Trailing, relatedBy: .Equal, toItem: subview, attribute: .Trailing, multiplier: 1.0, constant: 0.0))

Answer 2

正如@rjobidon 提到的，您应该使用以下代码 (Swift3)

    let view = UIView() // existing view

    let subview = UIView()
    subview.setTranslatesAutoresizingMaskIntoConstraints(false)

    view.addSubview(subview)

    NSLayoutConstraint(item: subview, attribute: .top, relatedBy: .equal, toItem: view, attribute: .top, multiplier: 1.0, constant: 0.0).isActive = true
    NSLayoutConstraint(item: subview, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leading, multiplier: 1.0, constant: 0.0).isActive = true
    NSLayoutConstraint(item: view, attribute: .bottom, relatedBy: .equal, toItem: subview, attribute: .bottom, multiplier: 1.0, constant: 0.0).isActive = true
    NSLayoutConstraint(item: view, attribute: .trailing, relatedBy: .equal, toItem: subview, attribute: .trailing, multiplier: 1.0, constant: 0.0).isActive = true

Answer 3

iOS13，swift5

首先，您添加这段代码

    subview.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(subview)

然后，在 iOS 的较新版本中有两种方法可以做到这一点。

和NSLayoutConstraintclass

NSLayoutConstraint(item: subview, attribute: .top, relatedBy: .equal, toItem: view, attribute: .top, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: subview, attribute: .bottom, relatedBy: .equal, toItem: view, attribute: .bottom, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: subview, attribute: .left, relatedBy: .equal, toItem: view, attribute: .left, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: subview, attribute: .right, relatedBy: .equal, toItem: view, attribute: .right, multiplier: 1, constant: 0).isActive = true

与 NSLayoutAnchor class（更简洁）

subview.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
subview.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
subview.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
subview.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true

无论哪种方式，在 iOS 8 及更高版本上，Apple 建议使用 isActive() 而不是直接向视图添加约束。

此外，我认为 NSLayoutAnchor 方法的目的是与 NSLayoutConstraint 相比更加简洁和可读。

Answer 4

您也可以像这样激活约束：

let view = UIView() // existing view

let subview = UIView()
subview.translatesAutoresizingMaskIntoConstraints = false

view.addSubview(subview)


NSLayoutConstraint.activate([
                view.leadingAnchor.constraint(equalTo: subview.leadingAnchor),
                view.trailingAnchor.constraint(equalTo: subview.trailingAnchor),
                view.topAnchor.constraint(equalTo: subview.topAnchor),
                view.bottomAnchor.constraint(equalTo: subview.bottomAnchor)
            ])

通过 Swift 中的代码自动布局适合父级

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