Swift 约束在调整约束高度后无法移回屏幕底部

Question

我有一个使用自动布局的按钮位于屏幕底部。我正在尝试使按钮调整位置始终位于键盘上方。到目前为止，我已经能够让按钮向上移动，但我无法让按钮的位置重置。

我完全以编程方式做所有事情，我根本不使用故事板。没有出口的解决方案将不胜感激。

我的viewDidLoad函数（只展示与按钮移动相关的逻辑）

NotificationCenter.default.addObserver(self, selector: #selector(keyboardMovedUp(notification:)), name: UIResponder.keyboardWillShowNotification, object: nil)

NotificationCenter.default.addObserver(self, selector: #selector(keyboardMovedDown(notification:)), name: UIResponder.keyboardWillHideNotification, object: nil)

keyboardMovedUp函数

@objc
func keyboardMovedUp(notification: Notification) {
    if let userInfo = notification.userInfo {
        let endFrame = (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue
        let viewEndFrame = view.convert(endFrame!, from: view.window)
        let endFrameY = endFrame?.origin.y ?? 0
        let animationRate = (userInfo[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber)?.doubleValue
        let animationCurveRawNSM = userInfo[UIResponder.keyboardAnimationCurveUserInfoKey] as? NSNumber
        let animationCurveRaw = animationCurveRawNSM?.uintValue ?? UIView.AnimationOptions.curveEaseInOut.rawValue
        let animationCurve: UIView.AnimationOptions = UIView.AnimationOptions(rawValue: animationCurveRaw)

        self.moveUp = self.continueButton.bottomAnchor.constraint(equalTo: self.view.bottomAnchor, constant: -viewEndFrame.origin.y)
        self.moveUp?.isActive = true

        UIView.animate(withDuration: animationRate!, delay: TimeInterval(0), options: animationCurve, animations: {
            self.view.layoutIfNeeded()
        }, completion: nil)
    }
}

和我的 keyboardMovedDown 函数

@objc
func keyboardMovedDown(notification: Notification) {
    if let userInfo = notification.userInfo {
        let endFrame = (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue

        self.moveUp?.isActive = false
        self.moveDown = self.continueButton.bottomAnchor.constraint(equalTo: self.view.bottomAnchor, constant: -20)
        self.moveDown?.isActive = true


        UIView.animate(withDuration: 0.25) {
            self.view.layoutIfNeeded()
        }
    }
}

使用此代码，当键盘显示时，按钮会向上移动，但一旦键盘被重置，按钮不会移动位置。

我可以通过修改按钮的 origin.y 参数使代码正常工作，但我听说这会导致自动版式出现兼容性问题。

编辑：@IchBinStudenten 这是我当前代码经过您的更改后的样子

func viewDidLoad() {
     self.moveUp = self.continueButton.bottomAnchor.constraint(equalTo: self.view.bottomAnchor, constant: -20)
     self.moveUp?.isActive = true

}

@objc
func keyboardMoved(notification: Notification) {
    if let userInfo = notification.userInfo {
        let endFrame = (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue
        let viewEndFrame = view.convert(endFrame!, from: view.window)
        let endFrameY = endFrame?.origin.y ?? 0
        let animationRate = (userInfo[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber)?.doubleValue
        let animationCurveRawNSM = userInfo[UIResponder.keyboardAnimationCurveUserInfoKey] as? NSNumber
        let animationCurveRaw = animationCurveRawNSM?.uintValue ?? UIView.AnimationOptions.curveEaseInOut.rawValue
        let animationCurve: UIView.AnimationOptions = UIView.AnimationOptions(rawValue: animationCurveRaw)

        self.moveUp?.constant = -viewEndFrame.height - 20

        UIView.animate(withDuration: animationRate!, delay: TimeInterval(0), options: animationCurve, animations: {
            self.view.layoutIfNeeded()
        }, completion: nil)
    }
}

@objc
func keyboardMovedDown(notification: Notification) {
    if let userInfo = notification.userInfo {

        self.moveUp?.constant = 0

        UIView.animate(withDuration: 0.25) {
            self.view.layoutIfNeeded()
        }
    }
}

Answer 1

使用1个约束就可以达到你想要的效果。无论如何，您正在使用一个约束。设置 self.moveUp 在键盘向上移动时激活，并更改其值

self.moveUp?.constant = -20.0

当键盘向下移动时。为了使代码更简洁，只需在 class 中创建一些变量来保留对 self.continueButton.bottomAnchor.constraint(equalTo:self.view.bottomAnchor) 的引用，这样您就可以修改它的 constant 属性只要。例如：

let keyboardConstraint: NSLayoutConstraint

override func viewDidLoad() {
   self.keyboardConstraint = self.continueButton.bottomAnchor.constraint(equalTo: self.view.bottomAnchor)
   self.keyboardConstraint.isActive = true
}

@objc
func keyboardMovedUp(notification: Notification) {
        /// ...your code 
        self.keyboardConstraint.constant = -viewEndFrame.origin.y

        UIView.animate(withDuration: animationRate!, delay: TimeInterval(0), options: animationCurve, animations: {
            self.view.layoutIfNeeded()
        }, completion: nil)
    }
}

@objc
func keyboardMovedDown(notification: Notification) {
    if let userInfo = notification.userInfo {
        let endFrame = (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue

        self.keyboardConstraint.constant = -20.0

        UIView.animate(withDuration: 0.25) {
            self.view.layoutIfNeeded()
        }
    }
}

另一种选择是通过 CocoaPods 安装 IQKeyboardManager，它会为您管理这一切。

如果这能解决您的问题，请告诉我。

Answer 2

为方便起见，将约束设为一个实例属性:

private lazy var continueButtonBottomAnchor = continueButton.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -bottomSafeArea)

将其添加为子视图时在 loadView 中激活它：

continueButtonBottomAnchor.isActive = true

bottomSafeArea 是计算得到的属性因为我假设您想将按钮放置在底部安全区域。计算属性不存储值（仅计算），因此您可以在这些通知中使用正确的值延迟访问它们。

@objc private func keyboardMovedUp(_ notification: Notification) {
    guard let keyboardFrame = notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue else {
        return
    }
    continueButtonBottomAnchor.constant = -keyboardFrame.cgRectValue.height   
    UIView.animate(withDuration: 0, animations: {
        self.view.layoutIfNeeded()
    })
}

@objc private func keyboardMovedDown() {
    continueBUttonBottomAnchor.constant = -bottomSafeArea // using our computed property
    UIView.animate(withDuration: 0, animations: {
        self.view.layoutIfNeeded()
    })
}

与接受的答案不同，不要添加您自己的或尝试获取动画参数（持续时间和时间）；通过在通知内设置动画，这些参数将自动应用，因此您的约束将与键盘完美同步移动。

Swift 约束在调整约束高度后无法移回屏幕底部

Swift constraints unable to move back to bottom of screen after adjusting constraint height

ios

swift

swift5