我看到几乎每个人都在情节提要中的 scroll view 中使用虚拟视图。 滚动视图本身不是视图吗？
此官方Apple docs link中指出：
对于大多数常见的布局任务，如果您使用虚拟视图或布局组来包含滚动视图的内容，则逻辑变得容易得多。
我确实尝试直接使用滚动视图而不是使用内容视图（虚拟视图）作为中介，但发现自己处于便秘状态，但我没有知道为什么。
这是我的问题：
答案 0 :(得分：1)
查看是否在滚动视图中使用内容视图，在使用自动布局的情况下，无需以编程方式计算和设置滚动视图的内容大小，因为UI元素将自动布局约束设置为内容视图，并且内容视图将更改根据用户界面元素内容的大小。滚动视图具有两种不同的功能，一种是其框架，另一种是其内容大小。因此，如果不使用内容视图层，则必须根据UI元素内容手动设置滚动视图的内容大小。请检查：https://medium.com/@pradeep_chauhan/how-to-configure-a-uiscrollview-with-auto-layout-in-interface-builder-218dcb4022d7
答案 1 :(得分：1)
通常，元素是动态添加的。许多人发现将它们添加到“内容视图”比将它们直接添加到滚动视图更容易。
我个人认为直接方法更容易。
没有虚拟/内容视图，您只需将元素限制为滚动视图本身，而不是内容视图。
这里有两个例子。 ContentScrollViewController和DirectScrollViewController。如您所见，它们几乎是相同的。这实际上是一个优先选择的问题……您 start 使用的任何一种方法可能都是您喜欢的方法。注意：出于演示的目的，我经常给元素提供完全不同的背景颜色，以使其易于查看布局框架。
内容查看方法：
class ContentScrollViewController: UIViewController {
let topLabel: UILabel = {
let v = UILabel()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .green
v.text = "Top Label"
return v
}()
let bottomLabel: UILabel = {
let v = UILabel()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .green
v.text = "Top Label"
return v
}()
let contentView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .orange
return v
}()
let scrollView: UIScrollView = {
let v = UIScrollView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .red
return v
}()
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(scrollView)
scrollView.addSubview(contentView)
contentView.addSubview(topLabel)
contentView.addSubview(bottomLabel)
NSLayoutConstraint.activate([
// constrain scrollView to all 4 sides with 20-pts padding
scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20.0),
scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -20.0),
scrollView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 20.0),
scrollView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -20.0),
// constrain contentView to all 4 sides of scrollView with 8-pts padding
contentView.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 8.0),
contentView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: -8.0),
contentView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor, constant: 8.0),
contentView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor, constant: -8.0),
// constrain topLabel 0-pts to top and leading of contentView
topLabel.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 0.0),
topLabel.leadingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: 0.0),
// constrain bottomLabel's top 800-pts from bottom of topLabel
bottomLabel.topAnchor.constraint(equalTo: topLabel.bottomAnchor, constant: 800.0),
// constrain bottomLabel's leading 600-pts from trailing of topLabel
bottomLabel.leadingAnchor.constraint(equalTo: topLabel.trailingAnchor, constant: 600.0),
// constrain bottomLabel 0-pts to bottom and trailing of contentView
bottomLabel.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: 0.0),
bottomLabel.trailingAnchor.constraint(equalTo: contentView.trailingAnchor, constant: 0.0),
])
}
}
直接方法：
class DirectScrollViewController: UIViewController {
let topLabel: UILabel = {
let v = UILabel()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .green
v.text = "Top Label"
return v
}()
let bottomLabel: UILabel = {
let v = UILabel()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .green
v.text = "Top Label"
return v
}()
let scrollView: UIScrollView = {
let v = UIScrollView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .red
return v
}()
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(scrollView)
scrollView.addSubview(topLabel)
scrollView.addSubview(bottomLabel)
NSLayoutConstraint.activate([
// constrain scrollView to all 4 sides with 20-pts padding
scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20.0),
scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -20.0),
scrollView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 20.0),
scrollView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -20.0),
// constrain topLabel 8-pts to top and leading of scrollView
topLabel.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 8.0),
topLabel.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor, constant: 8.0),
// constrain bottomLabel's top 800-pts from bottom of topLabel
bottomLabel.topAnchor.constraint(equalTo: topLabel.bottomAnchor, constant: 800.0),
// constrain bottomLabel's leading 600-pts from trailing of topLabel
bottomLabel.leadingAnchor.constraint(equalTo: topLabel.trailingAnchor, constant: 600.0),
// constrain bottomLabel 8-pts to bottom and trailing of scrollView
bottomLabel.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: -8.0),
bottomLabel.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor, constant: -8.0),
])
}
}