ios - 将 UIView 设置为键盘高度

Question

我想将我的 View 底部约束设置为等于键盘高度。键盘在 VC 的生命周期中始终处于事件状态。

但是，当我的 VC 正在加载时，我的 View 以一种奇怪的方式改变了它的高度(如我在 gif 中所示)

在 IB 中，keyboardHeigthConstraint 是 Bottom Layout Guide Top 和我的 View 的约束，并且等于 0

 @IBOutlet weak var keyboardHeigthConstraint: NSLayoutConstraint!

   override func viewDidLoad() {
        super.viewDidLoad()
        cardNumberTextField.becomeFirstResponder()

        NotificationCenter.default.addObserver(self, selector: #selector(handleKeyboardNotification), name: NSNotification.Name.UIKeyboardWillChangeFrame , object: nil)
    }

func handleKeyboardNotification(notification: NSNotification) {

    if let userInfo = notification.userInfo {
        let keyboardFrame: CGRect = (userInfo[UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue

        DispatchQueue.main.async {
            self.keyboardHeigthConstraint.constant = keyboardFrame.size.height
            self.view.layoutIfNeeded()
        }
    }

什么会导致这种奇怪的行为？

Answer 1

您的代码中存在一些问题:

• cardNumberTextField.becomeFirstResponder() 应该在 viewWillAppear 中调用；
• 在订阅键盘通知后调用 cardNumberTextField.becomeFirstResponder()；
• 取消订阅 viewDidDisappear 中的键盘通知；
• 更新约束而不将其包装在 DispatchQueue.main.async 中。

我认为它应该有所帮助。

@IBOutlet weak var keyboardHeigthConstraint: NSLayoutConstraint!

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    NotificationCenter.default.addObserver(self, selector: #selector(handleKeyboardNotification), name: NSNotification.Name.UIKeyboardWillChangeFrame, object: nil)
    cardNumberTextField.becomeFirstResponder()
}

override func viewDidDisappear(_ animated: Bool) {
    NotificationCenter.default.removeObserver(self)
    super.viewDidDisappear(animated)
}

func handleKeyboardNotification(notification: NSNotification) {
    guard let userInfo = notification.userInfo,
        let frameValue = userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue else {

        return
    }

    let keyboardFrame = frameValue.cgRectValue
    keyboardHeigthConstraint.constant = keyboardFrame.height
    view.layoutIfNeeded()
}