AutoLayout 约束以适应矩形内的视图，保留一定的纵横比（以编程方式）
AutoLayout constraints to fit view inside rectangle, preserving a certain aspect ratio (programmatically)
我想将图像放入应具有特定纵横比的矩形内。不管它是什么，它都应该找到适合矩形的形式。我在情节提要中玩了一下，得到了这个：
带虚线边框的优先级较低（250）。
这在故事板中有效。但是，我需要以编程方式创建这些约束，所以我这样尝试（我正在使用 SnapKit，它只是提供更好的 AutoLayout 语法。它应该是不言自明的）：
let topView = UIView()
topView.translatesAutoresizingMaskIntoConstraints = false
topView.backgroundColor = .gray
view.addSubview(topView)
topView.snp.makeConstraints { (make) in
make.top.equalToSuperview()
make.left.equalToSuperview()
make.trailing.equalToSuperview()
make.height.equalTo(250)
}
// This view should have a specific aspect ratio and fit inside topView
let holderView = UIView()
holderView.translatesAutoresizingMaskIntoConstraints = false
holderView.backgroundColor = .red
topView.addSubview(holderView)
holderView.snp.makeConstraints { (make) in
make.center.equalToSuperview() // If I remove this one, there's no auto-layout issue, but then it's offset
make.edges.equalToSuperview().priority(250) // sets leading, trailing, top and bottom
make.edges.greaterThanOrEqualToSuperview().priority(1000)
make.width.equalTo(holderView.snp.height).multipliedBy(3/2)
}
如果您将其粘贴到一个空的 ViewController 中并启动它，您会遇到这些问题：
2018-03-16 15:38:50.188867+0100 DemoProject[11298:850932] [LayoutConstraints] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want.
Try this:
(1) look at each constraint and try to figure out which you don't expect;
(2) find the code that added the unwanted constraint or constraints and fix it.
"<SnapKit.LayoutConstraint:0x6000000a7c80@ViewController.swift#24 UIView:0x7fcd82d12440.left == UIView:0x7fcd82d12640.left>",
"<SnapKit.LayoutConstraint:0x6000000a7ce0@ViewController.swift#25 UIView:0x7fcd82d12440.trailing == UIView:0x7fcd82d12640.trailing>",
"<SnapKit.LayoutConstraint:0x6000000a7d40@ViewController.swift#26 UIView:0x7fcd82d12440.height == 250.0>",
"<SnapKit.LayoutConstraint:0x6000000a7da0@ViewController.swift#35 UIView:0x7fcd8580dad0.centerX == UIView:0x7fcd82d12440.centerX>",
"<SnapKit.LayoutConstraint:0x6000000a7e00@ViewController.swift#35 UIView:0x7fcd8580dad0.centerY == UIView:0x7fcd82d12440.centerY>",
"<SnapKit.LayoutConstraint:0x6000000a8580@ViewController.swift#37 UIView:0x7fcd8580dad0.top >= UIView:0x7fcd82d12440.top>",
"<SnapKit.LayoutConstraint:0x6000000a8a60@ViewController.swift#37 UIView:0x7fcd8580dad0.right >= UIView:0x7fcd82d12440.right>",
"<SnapKit.LayoutConstraint:0x6000000a9360@ViewController.swift#38 UIView:0x7fcd8580dad0.width == UIView:0x7fcd8580dad0.height>",
"<NSLayoutConstraint:0x600000092cf0 'UIView-Encapsulated-Layout-Width' UIView:0x7fcd82d12640.width == 414 (active)>"
Will attempt to recover by breaking constraint <SnapKit.LayoutConstraint:0x6000000a9360@ViewController.swift#38 UIView:0x7fcd8580dad0.width == UIView:0x7fcd8580dad0.height>
当我删除居中约束时，这并没有出现make.center.equalToSuperview()。但是，它放错了地方。
故事板和我的代码有什么不同？我真的不明白这一点。我也尝试使用默认的 swift 语法，结果完全一样。所以我不认为 SnapKit
有问题
有什么想法吗？谢谢你们的帮助。如果您需要更多信息，请告诉我。
编辑：我搞混了。这与图像及其纵横比无关。它只是一个 UIView 应该保持特定的纵横比，同时适合一个矩形。实际图像将被放入 holderView。抱歉
好的 - 这是一种方法。
获取子视图的 "native" 大小，计算 "aspect fit" 比率 - 即适合父视图的宽度或高度的比率，并适当缩放其他维度。
然后，使用 centerXAnchor 和 centerYAnchor 定位子视图，并使用 widthAnchor 和 heightAnchor 调整其大小。
注意：如果您尝试放置 图像，请根据图像大小计算宽高比大小，将图像放入图像视图，设置图像视图比例模式 fill，最后将约束应用于图像视图。
你应该能够运行这个例子as-is。只需调整顶部的 "native" 大小值，看看它如何使子视图适合父视图。
public class AspectFitViewController : UIViewController {
// "native" size for the holderView
let hViewWidth: CGFloat = 700.0
let hViewHeight: CGFloat = 200.0
let topView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = UIColor.blue
return v
}()
let holderView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = UIColor.cyan
return v
}()
public override func viewDidLoad() {
super.viewDidLoad()
view.bounds = CGRect(x: 0, y: 0, width: 400, height: 600)
view.backgroundColor = .yellow
// add topView
view.addSubview(topView)
// pin topView to leading / top / trailing
topView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0.0).isActive = true
topView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0.0).isActive = true
topView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0.0).isActive = true
// explicit height for topView
topView.heightAnchor.constraint(equalToConstant: 250.0).isActive = true
// add holderView to topView
topView.addSubview(holderView)
// center X and Y
holderView.centerXAnchor.constraint(equalTo: topView.centerXAnchor, constant: 0.0).isActive = true
holderView.centerYAnchor.constraint(equalTo: topView.centerYAnchor, constant: 0.0).isActive = true
// holderView's width and height will be calculated in viewDidAppear
// after topView has been laid-out by the auto-layout engine
}
public override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
let aspectWidth = topView.bounds.size.width / hViewWidth
let aspectHeight = topView.bounds.size.height / hViewHeight
let aspectFit = min(aspectWidth, aspectHeight)
let newWidth = hViewWidth * aspectFit
let newHeight = hViewHeight * aspectFit
holderView.widthAnchor.constraint(equalToConstant: newWidth).isActive = true
holderView.heightAnchor.constraint(equalToConstant: newHeight).isActive = true
}
}
编辑：
经过澄清...这只能通过约束来完成。关键是 "Priority 1000" top 和 leading 约束必须 .greaterThanOrEqual 为零， bottom 和 trailing 约束必须 .lessThanOrEqual 归零。
public class AspectFitViewController : UIViewController {
// "native" size for the holderView
let hViewWidth: CGFloat = 700.0
let hViewHeight: CGFloat = 200.0
let topView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = UIColor.blue
return v
}()
let holderView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = UIColor.cyan
return v
}()
public override func viewDidLoad() {
super.viewDidLoad()
view.bounds = CGRect(x: 0, y: 0, width: 400, height: 600)
view.backgroundColor = .yellow
// add topView
view.addSubview(topView)
// pin topView to leading / top / trailing
topView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0.0).isActive = true
topView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0.0).isActive = true
topView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0.0).isActive = true
// explicit height for topView
topView.heightAnchor.constraint(equalToConstant: 250.0).isActive = true
// add holderView to topView
topView.addSubview(holderView)
// center X and Y
holderView.centerXAnchor.constraint(equalTo: topView.centerXAnchor, constant: 0.0).isActive = true
holderView.centerYAnchor.constraint(equalTo: topView.centerYAnchor, constant: 0.0).isActive = true
// aspect ratio size
holderView.widthAnchor.constraint(equalTo: holderView.heightAnchor, multiplier: hViewWidth / hViewHeight).isActive = true
// two constraints for each side...
// the .equal constraints need .defaultLow priority
// top and leading constraints must be .greaterThanOrEqual to 0
// bottom and trailing constraints must be .lessThanOrEqual to 0
let topA = NSLayoutConstraint(item: holderView, attribute: .top, relatedBy: .greaterThanOrEqual, toItem: topView, attribute: .top, multiplier: 1.0, constant: 0.0)
let topB = NSLayoutConstraint(item: holderView, attribute: .top, relatedBy: .equal, toItem: topView, attribute: .top, multiplier: 1.0, constant: 0.0)
let bottomA = NSLayoutConstraint(item: holderView, attribute: .bottom, relatedBy: .lessThanOrEqual, toItem: topView, attribute: .bottom, multiplier: 1.0, constant: 0.0)
let bottomB = NSLayoutConstraint(item: holderView, attribute: .bottom, relatedBy: .equal, toItem: topView, attribute: .bottom, multiplier: 1.0, constant: 0.0)
let leadingA = NSLayoutConstraint(item: holderView, attribute: .leading, relatedBy: .greaterThanOrEqual, toItem: topView, attribute: .leading, multiplier: 1.0, constant: 0.0)
let leadingB = NSLayoutConstraint(item: holderView, attribute: .leading, relatedBy: .equal, toItem: topView, attribute: .leading, multiplier: 1.0, constant: 0.0)
let trailingA = NSLayoutConstraint(item: holderView, attribute: .trailing, relatedBy: .lessThanOrEqual, toItem: topView, attribute: .trailing, multiplier: 1.0, constant: 0.0)
let trailingB = NSLayoutConstraint(item: holderView, attribute: .trailing, relatedBy: .equal, toItem: topView, attribute: .trailing, multiplier: 1.0, constant: 0.0)
topB.priority = .defaultLow
bottomB.priority = .defaultLow
leadingB.priority = .defaultLow
trailingB.priority = .defaultLow
NSLayoutConstraint.activate([
topA, topB,
bottomA, bottomB,
leadingA, leadingB,
trailingA, trailingB
])
}
}
我想将图像放入应具有特定纵横比的矩形内。不管它是什么，它都应该找到适合矩形的形式。我在情节提要中玩了一下，得到了这个：
带虚线边框的优先级较低（250）。
这在故事板中有效。但是，我需要以编程方式创建这些约束，所以我这样尝试（我正在使用 SnapKit，它只是提供更好的 AutoLayout 语法。它应该是不言自明的）：
let topView = UIView()
topView.translatesAutoresizingMaskIntoConstraints = false
topView.backgroundColor = .gray
view.addSubview(topView)
topView.snp.makeConstraints { (make) in
make.top.equalToSuperview()
make.left.equalToSuperview()
make.trailing.equalToSuperview()
make.height.equalTo(250)
}
// This view should have a specific aspect ratio and fit inside topView
let holderView = UIView()
holderView.translatesAutoresizingMaskIntoConstraints = false
holderView.backgroundColor = .red
topView.addSubview(holderView)
holderView.snp.makeConstraints { (make) in
make.center.equalToSuperview() // If I remove this one, there's no auto-layout issue, but then it's offset
make.edges.equalToSuperview().priority(250) // sets leading, trailing, top and bottom
make.edges.greaterThanOrEqualToSuperview().priority(1000)
make.width.equalTo(holderView.snp.height).multipliedBy(3/2)
}
如果您将其粘贴到一个空的 ViewController 中并启动它，您会遇到这些问题：
2018-03-16 15:38:50.188867+0100 DemoProject[11298:850932] [LayoutConstraints] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want.
Try this:
(1) look at each constraint and try to figure out which you don't expect;
(2) find the code that added the unwanted constraint or constraints and fix it.
"<SnapKit.LayoutConstraint:0x6000000a7c80@ViewController.swift#24 UIView:0x7fcd82d12440.left == UIView:0x7fcd82d12640.left>",
"<SnapKit.LayoutConstraint:0x6000000a7ce0@ViewController.swift#25 UIView:0x7fcd82d12440.trailing == UIView:0x7fcd82d12640.trailing>",
"<SnapKit.LayoutConstraint:0x6000000a7d40@ViewController.swift#26 UIView:0x7fcd82d12440.height == 250.0>",
"<SnapKit.LayoutConstraint:0x6000000a7da0@ViewController.swift#35 UIView:0x7fcd8580dad0.centerX == UIView:0x7fcd82d12440.centerX>",
"<SnapKit.LayoutConstraint:0x6000000a7e00@ViewController.swift#35 UIView:0x7fcd8580dad0.centerY == UIView:0x7fcd82d12440.centerY>",
"<SnapKit.LayoutConstraint:0x6000000a8580@ViewController.swift#37 UIView:0x7fcd8580dad0.top >= UIView:0x7fcd82d12440.top>",
"<SnapKit.LayoutConstraint:0x6000000a8a60@ViewController.swift#37 UIView:0x7fcd8580dad0.right >= UIView:0x7fcd82d12440.right>",
"<SnapKit.LayoutConstraint:0x6000000a9360@ViewController.swift#38 UIView:0x7fcd8580dad0.width == UIView:0x7fcd8580dad0.height>",
"<NSLayoutConstraint:0x600000092cf0 'UIView-Encapsulated-Layout-Width' UIView:0x7fcd82d12640.width == 414 (active)>"
Will attempt to recover by breaking constraint <SnapKit.LayoutConstraint:0x6000000a9360@ViewController.swift#38 UIView:0x7fcd8580dad0.width == UIView:0x7fcd8580dad0.height>
当我删除居中约束时，这并没有出现make.center.equalToSuperview()。但是，它放错了地方。
故事板和我的代码有什么不同？我真的不明白这一点。我也尝试使用默认的 swift 语法，结果完全一样。所以我不认为 SnapKit
有什么想法吗？谢谢你们的帮助。如果您需要更多信息，请告诉我。
编辑：我搞混了。这与图像及其纵横比无关。它只是一个 UIView 应该保持特定的纵横比，同时适合一个矩形。实际图像将被放入 holderView。抱歉
好的 - 这是一种方法。
获取子视图的 "native" 大小，计算 "aspect fit" 比率 - 即适合父视图的宽度或高度的比率，并适当缩放其他维度。
然后，使用 centerXAnchor 和 centerYAnchor 定位子视图，并使用 widthAnchor 和 heightAnchor 调整其大小。
注意：如果您尝试放置 图像，请根据图像大小计算宽高比大小，将图像放入图像视图，设置图像视图比例模式 fill，最后将约束应用于图像视图。
你应该能够运行这个例子as-is。只需调整顶部的 "native" 大小值，看看它如何使子视图适合父视图。
public class AspectFitViewController : UIViewController {
// "native" size for the holderView
let hViewWidth: CGFloat = 700.0
let hViewHeight: CGFloat = 200.0
let topView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = UIColor.blue
return v
}()
let holderView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = UIColor.cyan
return v
}()
public override func viewDidLoad() {
super.viewDidLoad()
view.bounds = CGRect(x: 0, y: 0, width: 400, height: 600)
view.backgroundColor = .yellow
// add topView
view.addSubview(topView)
// pin topView to leading / top / trailing
topView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0.0).isActive = true
topView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0.0).isActive = true
topView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0.0).isActive = true
// explicit height for topView
topView.heightAnchor.constraint(equalToConstant: 250.0).isActive = true
// add holderView to topView
topView.addSubview(holderView)
// center X and Y
holderView.centerXAnchor.constraint(equalTo: topView.centerXAnchor, constant: 0.0).isActive = true
holderView.centerYAnchor.constraint(equalTo: topView.centerYAnchor, constant: 0.0).isActive = true
// holderView's width and height will be calculated in viewDidAppear
// after topView has been laid-out by the auto-layout engine
}
public override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
let aspectWidth = topView.bounds.size.width / hViewWidth
let aspectHeight = topView.bounds.size.height / hViewHeight
let aspectFit = min(aspectWidth, aspectHeight)
let newWidth = hViewWidth * aspectFit
let newHeight = hViewHeight * aspectFit
holderView.widthAnchor.constraint(equalToConstant: newWidth).isActive = true
holderView.heightAnchor.constraint(equalToConstant: newHeight).isActive = true
}
}
编辑：
经过澄清...这只能通过约束来完成。关键是 "Priority 1000" top 和 leading 约束必须 .greaterThanOrEqual 为零， bottom 和 trailing 约束必须 .lessThanOrEqual 归零。
public class AspectFitViewController : UIViewController {
// "native" size for the holderView
let hViewWidth: CGFloat = 700.0
let hViewHeight: CGFloat = 200.0
let topView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = UIColor.blue
return v
}()
let holderView: UIView = {
let v = UIView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = UIColor.cyan
return v
}()
public override func viewDidLoad() {
super.viewDidLoad()
view.bounds = CGRect(x: 0, y: 0, width: 400, height: 600)
view.backgroundColor = .yellow
// add topView
view.addSubview(topView)
// pin topView to leading / top / trailing
topView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0.0).isActive = true
topView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0.0).isActive = true
topView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0.0).isActive = true
// explicit height for topView
topView.heightAnchor.constraint(equalToConstant: 250.0).isActive = true
// add holderView to topView
topView.addSubview(holderView)
// center X and Y
holderView.centerXAnchor.constraint(equalTo: topView.centerXAnchor, constant: 0.0).isActive = true
holderView.centerYAnchor.constraint(equalTo: topView.centerYAnchor, constant: 0.0).isActive = true
// aspect ratio size
holderView.widthAnchor.constraint(equalTo: holderView.heightAnchor, multiplier: hViewWidth / hViewHeight).isActive = true
// two constraints for each side...
// the .equal constraints need .defaultLow priority
// top and leading constraints must be .greaterThanOrEqual to 0
// bottom and trailing constraints must be .lessThanOrEqual to 0
let topA = NSLayoutConstraint(item: holderView, attribute: .top, relatedBy: .greaterThanOrEqual, toItem: topView, attribute: .top, multiplier: 1.0, constant: 0.0)
let topB = NSLayoutConstraint(item: holderView, attribute: .top, relatedBy: .equal, toItem: topView, attribute: .top, multiplier: 1.0, constant: 0.0)
let bottomA = NSLayoutConstraint(item: holderView, attribute: .bottom, relatedBy: .lessThanOrEqual, toItem: topView, attribute: .bottom, multiplier: 1.0, constant: 0.0)
let bottomB = NSLayoutConstraint(item: holderView, attribute: .bottom, relatedBy: .equal, toItem: topView, attribute: .bottom, multiplier: 1.0, constant: 0.0)
let leadingA = NSLayoutConstraint(item: holderView, attribute: .leading, relatedBy: .greaterThanOrEqual, toItem: topView, attribute: .leading, multiplier: 1.0, constant: 0.0)
let leadingB = NSLayoutConstraint(item: holderView, attribute: .leading, relatedBy: .equal, toItem: topView, attribute: .leading, multiplier: 1.0, constant: 0.0)
let trailingA = NSLayoutConstraint(item: holderView, attribute: .trailing, relatedBy: .lessThanOrEqual, toItem: topView, attribute: .trailing, multiplier: 1.0, constant: 0.0)
let trailingB = NSLayoutConstraint(item: holderView, attribute: .trailing, relatedBy: .equal, toItem: topView, attribute: .trailing, multiplier: 1.0, constant: 0.0)
topB.priority = .defaultLow
bottomB.priority = .defaultLow
leadingB.priority = .defaultLow
trailingB.priority = .defaultLow
NSLayoutConstraint.activate([
topA, topB,
bottomA, bottomB,
leadingA, leadingB,
trailingA, trailingB
])
}
}