为啥UIView动画会改变View frame？
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【中文标题】为啥UIView动画会改变View frame？【英文标题】：Why does UIView animation change View frame?为什么UIView动画会改变View frame？ 【发布时间】：2017-11-15 05:53:15 【问题描述】：更新：我添加了一个显式调用，以在过渡的完成处理程序中设置“to”视图的框架。 这解决了“问题”，但没有回答为什么框架在隐藏时会发生变化的问题。这是新的动画调用。注意 - 我通过创建一个处理 spanSuperView() 和动画的函数来稍微清理代码，因此这与原始代码不完全匹配。要点已更新。我希望它对某人有所帮助，也许其他人知道为什么。
这是多次运行的动画：
func animateView(_ new: UIView)
UIView.transition(from: self.currentView, to: new, duration: 1, options: UIViewAnimationOptions.transitionFlipFromRight, completion: finished in
new.spanSuperView()
new.isHidden = false
self.currentView.isHidden = true
self.currentView = new
self.container.layoutIfNeeded()
)
动画现在在按钮切换方法中调用而不是重复：
@objc func viewChange(_ sender: UIButton)
print(sender.tag)
switch sender.tag
case 1 :
print("should look at view1")
print(currentView)
animateView(viewone)
case 2 :
print(currentView)
animateView(viewtwo)
case 3 :
print(currentView)
animateView(viewthree)
case 4 :
print(currentView)
animateView(viewfour)
default:
animateView(viewone)
这里是 spanSuperView()：
extension UIView
func spanSuperView()
guard superview != nil else return
self.topAnchor.constraint(equalTo: superview!.topAnchor).isActive = true
self.leadingAnchor.constraint(equalTo: superview!.leadingAnchor).isActive = true
self.widthAnchor.constraint(equalTo: superview!.widthAnchor, multiplier: 1.0).isActive = true
self.heightAnchor.constraint(equalTo: superview!.heightAnchor, multiplier: 1.0).isActive = true
self.translatesAutoresizingMaskIntoConstraints = false
另一个更新： 如果没有 UIView.transition（只显示 | 隐藏），则根本不会出现问题：
func animateView(_ new: UIView)
if new == currentView return
new.spanSuperView()
new.isHidden = false
self.currentView.isHidden = true
self.currentView = new
原始问题： 我正在尝试创建一个带有动画子视图的视图，用户可以通过单击按钮在它们之间切换。 这在第一次显示视图时工作正常，但子视图的框架在第一次后会发生变化，然后视图会在没有子视图的情况下进行动画处理。
这是操场的代码。我还创建了一个GIST
import UIKit
import PlaygroundSupport
class ButtonRow: UIView
var button1 = UIButton()
var button2 = UIButton()
var button3 = UIButton()
var button4 = UIButton()
var stackView = UIStackView()
func updateButtonLabels(_ texts:[String]? = ["1", "2", "3", "4"])
guard let texts = texts else return
let buttons = [button1, button2, button3, button4]
var i = 0
for btn in buttons
btn.setTitle(texts[i], for: .normal)
i += 1
override init(frame: CGRect)
super.init(frame: frame)
makeStack()
stackView.translatesAutoresizingMaskIntoConstraints = false
self.addSubview(stackView)
stackView.widthAnchor.constraint(equalTo: self.widthAnchor, multiplier: 1.0).isActive = true
stackView.heightAnchor.constraint(equalTo: self.heightAnchor, multiplier: 1.0).isActive = true
stackView.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
stackView.leadingAnchor.constraint(equalTo: self.leadingAnchor).isActive = true
func makeStack()
let buttons = [button1, button2, button3, button4]
for btn in buttons
btn.backgroundColor = .gray
btn.setTitleColor(.white, for: .normal)
btn.titleLabel?.font = UIFont.preferredFont(forTextStyle: UIFontTextStyle.headline)
btn.translatesAutoresizingMaskIntoConstraints = false
stackView = UIStackView(arrangedSubviews: buttons)
stackView.axis = .horizontal
stackView.distribution = .fillEqually
stackView.alignment = .fill
stackView.spacing = 10
override func layoutSubviews()
super.layoutSubviews()
stackView.frame = bounds
required init?(coder aDecoder: NSCoder)
fatalError("init(coder:) has not been implemented")
class MyViewController : UIViewController
// MARK: - Properties
var viewone = UIView()
var viewtwo = UIView()
var viewthree = UIView()
var viewfour = UIView()
var container = UIView()
var stackView = UIStackView()
var buttonRow = ButtonRow()
var currentView = UIView()
override func loadView()
let view = UIView()
view.backgroundColor = .white
self.view = view
setupStack()
override func viewWillLayoutSubviews()
print("will layout subviews")
//autolayout the stack view
let hSpacing: CGFloat = UIScreen.main.bounds.width/8
let wSpacing: CGFloat = UIScreen.main.bounds.width/10
if #available(ios 11.0, *)
let guide = self.view.safeAreaLayoutGuide
stackView.trailingAnchor.constraint(equalTo: guide.trailingAnchor, constant: -wSpacing).isActive = true
stackView.leadingAnchor.constraint(equalTo: guide.leadingAnchor, constant: wSpacing).isActive = true
stackView.topAnchor.constraint(equalTo: guide.topAnchor, constant: hSpacing).isActive = true
stackView.bottomAnchor.constraint(equalTo: guide.bottomAnchor, constant: -hSpacing).isActive = true
else
let margins = view.layoutMarginsGuide
stackView.trailingAnchor.constraint(equalTo: margins.trailingAnchor, constant: -wSpacing).isActive = true
stackView.leadingAnchor.constraint(equalTo: margins.leadingAnchor, constant: wSpacing).isActive = true
stackView.topAnchor.constraint(equalTo: margins.topAnchor, constant: hSpacing).isActive = true
stackView.bottomAnchor.constraint(equalTo: margins.bottomAnchor, constant: -hSpacing).isActive = true
func setupContainer()
container.backgroundColor = .yellow
viewone.backgroundColor = .blue
viewtwo.backgroundColor = .red
viewthree.backgroundColor = .green
viewfour.backgroundColor = .black
for vl in [viewone, viewtwo, viewthree, viewfour] as [UIView]
container.addSubview(vl)
vl.isHidden = true
vl.topAnchor.constraint(equalTo: container.topAnchor).isActive = true
vl.leadingAnchor.constraint(equalTo: container.leadingAnchor).isActive = true
vl.widthAnchor.constraint(equalTo: container.widthAnchor, multiplier: 1.0).isActive = true
vl.heightAnchor.constraint(equalTo: container.heightAnchor, multiplier: 1.0).isActive = true
vl.translatesAutoresizingMaskIntoConstraints = false
currentView = viewone
viewone.isHidden = false
func setupButtons()
buttonRow.updateButtonLabels()
var i = 1
for btn in [buttonRow.button1, buttonRow.button2, buttonRow.button3, buttonRow.button4]
btn.tag = i
btn.addTarget(self, action: #selector(viewChange), for: .touchUpInside)
i += 1
func setupStack()
setupButtons()
setupContainer()
stackView = UIStackView(arrangedSubviews: [container, buttonRow])
stackView.axis = .vertical
stackView.distribution = .fill
stackView.alignment = .fill
stackView.spacing = 10
stackView.translatesAutoresizingMaskIntoConstraints = false
// add some component constraints
let bHeight = buttonRow.heightAnchor.constraint(equalToConstant: 50)
stackView.addConstraints([bHeight])
view.addSubview(stackView)
// MARK: - Methods
@objc func viewChange(_ sender: UIButton)
print(sender.tag)
switch sender.tag
case 1 :
print("should look at view1")
print(currentView)
UIView.transition(from: self.currentView, to: self.viewone, duration: 1, options: UIViewAnimationOptions.transitionFlipFromRight, completion: nil)
currentView = viewone
viewone.isHidden = false
viewtwo.isHidden = true
viewthree.isHidden = true
viewfour.isHidden = true
case 2 :
print(currentView)
UIView.transition(from: self.currentView, to: self.viewtwo, duration: 1, options: UIViewAnimationOptions.transitionFlipFromRight, completion: nil)
currentView = viewtwo
viewone.isHidden = true
viewtwo.isHidden = false
viewthree.isHidden = true
viewfour.isHidden = true
case 3 :
print(currentView)
UIView.transition(from: self.currentView, to: self.viewthree, duration: 1, options: UIViewAnimationOptions.transitionFlipFromRight, completion: nil)
currentView = viewthree
viewone.isHidden = true
viewtwo.isHidden = true
viewthree.isHidden = false
viewfour.isHidden = true
case 4 :
print(currentView)
UIView.transition(from: self.currentView, to: self.viewfour, duration: 1, options: UIViewAnimationOptions.curveEaseInOut, completion: nil)
currentView = viewfour
viewone.isHidden = true
viewtwo.isHidden = true
viewthree.isHidden = true
viewfour.isHidden = false
default:
currentView = viewone
viewone.isHidden = false
viewtwo.isHidden = true
viewthree.isHidden = true
viewfour.isHidden = true
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()
打印语句显示仍然有一个 currentview 被识别，但它的帧从“frame = (0 0; 221 416)”变为“frame = (-77 -96; 0 0)":
will layout subviews
will layout subviews
1
should look at view1
<UIView: 0x7f7f42100630; frame = (0 0; 221 416); layer = <CALayer: 0x600000221440>>
2
<UIView: 0x7f7f42100630; frame = (0 0; 221 416); layer = <CALayer: 0x600000221440>>
3
<UIView: 0x7f7f421031f0; frame = (0 0; 221 416); layer = <CALayer: 0x600000221340>>
4
<UIView: 0x7f7f421033d0; frame = (0 0; 221 416); layer = <CALayer: 0x600000220140>>
1
should look at view1
<UIView: 0x7f7f421035b0; frame = (0 0; 221 416); layer = <CALayer: 0x600000220de0>>
2
<UIView: 0x7f7f42100630; frame = (-77 -96; 0 0); layer = <CALayer: 0x600000221440>>
3
<UIView: 0x7f7f421031f0; frame = (-77 -96; 0 0); layer = <CALayer: 0x600000221340>>
4
<UIView: 0x7f7f421033d0; frame = (-77 -96; 0 0); layer = <CALayer: 0x600000220140>>
注意：我创建了一个视频，但我似乎无法将其上传到 SO 或我的 Gist。
我不明白为什么框架会改变。什么给了？
【问题讨论】：
【参考方案1】：我认为每次你在 NSLayoutAnchor 上调用 constraint 时，你都会创建一个新的约束，所以我不会对在 2 次迭代后 UIKit 无法再解决约束感到惊讶。
您应该尝试为UIViewAlertForUnsatisfiableConstraints 添加一个符号断点，看看这是否是您的问题。
【讨论】：
我无法在操场上添加符号断点（全部变灰）。此外，它不应该有约束问题，因为子视图.translatesAutoresizingMaskIntoConstraints = false。但是，您的评论给了我一个想法，我在动画的完成块中明确设置了框架，现在它可以工作了。如果没有更详细的调试，我仍然不知道为什么。以上是关于为啥UIView动画会改变View frame？的主要内容，如果未能解决你的问题，请参考以下文章