我有一个UITextField，我想在点击它时放大它的宽度。我设置了约束并确保左侧约束的优先级低于我试图在右侧设置动画的约束。
这是我尝试使用的代码。
// move the input box
UIView.animateWithDuration(10.5, animations: {
self.nameInputConstraint.constant = 8
}, completion: {
(value: Bool) in
println(">>> move const")
})
这可行，但它似乎只是立即发生并且似乎没有任何动作。我尝试将其设置为 10 秒以确保我没有遗漏任何内容，但我得到了相同的结果。
nameInputConstraint 是我控制的约束的名称，它被拖动以从 IB 连接到我的类。
【问题讨论】：
标签： xcode swift constraints xcode6
您需要先更改约束，然后为更新设置动画。
这应该在 superview 中。
self.nameInputConstraint.constant = 8
斯威夫特 2
UIView.animateWithDuration(0.5) {
self.view.layoutIfNeeded()
}
Swift 3、4、5
UIView.animate(withDuration: 0.5) {
self.view.layoutIfNeeded()
}
【讨论】：
self。
SWIFT 4 及更高版本：
self.mConstraint.constant = 100.0
UIView.animate(withDuration: 0.3) {
self.view.layoutIfNeeded()
}
补全示例：
self.mConstraint.constant = 100
UIView.animate(withDuration: 0.3, animations: {
self.view.layoutIfNeeded()
}, completion: {res in
//Do something
})
【讨论】：
指出view.layoutIfNeeded() 仅适用于视图子视图，这一点非常重要。
因此，要为视图约束设置动画，重要的是在视图到动画superview上调用它，如下所示：
topConstraint.constant = heightShift
UIView.animate(withDuration: 0.3) {
// request layout on the *superview*
self.view.superview?.layoutIfNeeded()
}
一个简单布局的例子如下：
class MyClass {
/// Container view
let container = UIView()
/// View attached to container
let view = UIView()
/// Top constraint to animate
var topConstraint = NSLayoutConstraint()
/// Create the UI hierarchy and constraints
func createUI() {
container.addSubview(view)
// Create the top constraint
topConstraint = view.topAnchor.constraint(equalTo: container.topAnchor, constant: 0)
view.translatesAutoresizingMaskIntoConstraints = false
// Activate constaint(s)
NSLayoutConstraint.activate([
topConstraint,
])
}
/// Update view constraint with animation
func updateConstraint(heightShift: CGFloat) {
topConstraint.constant = heightShift
UIView.animate(withDuration: 0.3) {
// request layout on the *superview*
self.view.superview?.layoutIfNeeded()
}
}
}
【讨论】：
使用 Swift 5 和 iOS 12.3，根据您的需要，您可以选择以下 3 种方式之一来解决您的问题。
UIView的animate(withDuration:animations:)类方法animate(withDuration:animations:) 具有以下声明：
使用指定的持续时间对一个或多个视图进行动画更改。
class func animate(withDuration duration: TimeInterval, animations: @escaping () -> Void)
下面的 Playground 代码显示了animate(withDuration:animations:) 的可能实现，以便为自动布局约束的不断变化设置动画。
import UIKit
import PlaygroundSupport
class ViewController: UIViewController {
let textView = UITextView()
lazy var heightConstraint = textView.heightAnchor.constraint(equalToConstant: 50)
override func viewDidLoad() {
view.backgroundColor = .white
view.addSubview(textView)
textView.backgroundColor = .orange
textView.isEditable = false
textView.text = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
textView.translatesAutoresizingMaskIntoConstraints = false
textView.topAnchor.constraint(equalToSystemSpacingBelow: view.layoutMarginsGuide.topAnchor, multiplier: 1).isActive = true
textView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor).isActive = true
textView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor).isActive = true
heightConstraint.isActive = true
let tapGesture = UITapGestureRecognizer(target: self, action: #selector(doIt(_:)))
textView.addGestureRecognizer(tapGesture)
}
@objc func doIt(_ sender: UITapGestureRecognizer) {
heightConstraint.constant = heightConstraint.constant == 50 ? 150 : 50
UIView.animate(withDuration: 2) {
self.view.layoutIfNeeded()
}
}
}
PlaygroundPage.current.liveView = ViewController()
UIViewPropertyAnimator的init(duration:curve:animations:)初始化器和startAnimation()方法init(duration:curve:animations:) 有以下声明：
使用内置的 UIKit 时序曲线初始化动画器。
convenience init(duration: TimeInterval, curve: UIViewAnimationCurve, animations: (() -> Void)? = nil)
下面的 Playground 代码显示了 init(duration:curve:animations:) 和 startAnimation() 的可能实现，以便为自动布局约束的不断变化设置动画。
import UIKit
import PlaygroundSupport
class ViewController: UIViewController {
let textView = UITextView()
lazy var heightConstraint = textView.heightAnchor.constraint(equalToConstant: 50)
override func viewDidLoad() {
view.backgroundColor = .white
view.addSubview(textView)
textView.backgroundColor = .orange
textView.isEditable = false
textView.text = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
textView.translatesAutoresizingMaskIntoConstraints = false
textView.topAnchor.constraint(equalToSystemSpacingBelow: view.layoutMarginsGuide.topAnchor, multiplier: 1).isActive = true
textView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor).isActive = true
textView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor).isActive = true
heightConstraint.isActive = true
let tapGesture = UITapGestureRecognizer(target: self, action: #selector(doIt(_:)))
textView.addGestureRecognizer(tapGesture)
}
@objc func doIt(_ sender: UITapGestureRecognizer) {
heightConstraint.constant = heightConstraint.constant == 50 ? 150 : 50
let animator = UIViewPropertyAnimator(duration: 2, curve: .linear, animations: {
self.view.layoutIfNeeded()
})
animator.startAnimation()
}
}
PlaygroundPage.current.liveView = ViewController()
UIViewPropertyAnimator的runningPropertyAnimator(withDuration:delay:options:animations:completion:)类方法runningPropertyAnimator(withDuration:delay:options:animations:completion:) 具有以下声明：
创建并返回一个动画对象，该对象立即开始运行其动画。
class func runningPropertyAnimator(withDuration duration: TimeInterval, delay: TimeInterval, options: UIViewAnimationOptions = [], animations: @escaping () -> Void, completion: ((UIViewAnimatingPosition) -> Void)? = nil) -> Self
下面的 Playground 代码显示了runningPropertyAnimator(withDuration:delay:options:animations:completion:) 的可能实现，以便为自动布局约束的不断变化设置动画。
import UIKit
import PlaygroundSupport
class ViewController: UIViewController {
let textView = UITextView()
lazy var heightConstraint = textView.heightAnchor.constraint(equalToConstant: 50)
override func viewDidLoad() {
view.backgroundColor = .white
view.addSubview(textView)
textView.backgroundColor = .orange
textView.isEditable = false
textView.text = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
textView.translatesAutoresizingMaskIntoConstraints = false
textView.topAnchor.constraint(equalToSystemSpacingBelow: view.layoutMarginsGuide.topAnchor, multiplier: 1).isActive = true
textView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor).isActive = true
textView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor).isActive = true
heightConstraint.isActive = true
let tapGesture = UITapGestureRecognizer(target: self, action: #selector(doIt(_:)))
textView.addGestureRecognizer(tapGesture)
}
@objc func doIt(_ sender: UITapGestureRecognizer) {
heightConstraint.constant = heightConstraint.constant == 50 ? 150 : 50
UIViewPropertyAnimator.runningPropertyAnimator(withDuration: 2, delay: 0, options: [], animations: {
self.view.layoutIfNeeded()
})
}
}
PlaygroundPage.current.liveView = ViewController()
【讨论】：
就我而言，我只更新了自定义视图。
// DO NOT LIKE THIS
customView.layoutIfNeeded() // Change to view.layoutIfNeeded()
UIView.animate(withDuration: 0.5) {
customViewConstraint.constant = 100.0
customView.layoutIfNeeded() // Change to view.layoutIfNeeded()
}
【讨论】：
观看this。
视频说您只需添加self.view.layoutIfNeeded()，如下所示：
UIView.animate(withDuration: 1.0, animations: {
self.centerX.constant -= 75
self.view.layoutIfNeeded()
}, completion: nil)
【讨论】：