更新UIView中的中心Y和中心X约束

Question

我创建了一个UIVIew并将其添加到X和Y中心;

如果出现键盘，键盘将与View重叠。

如何更新约束并确保视图始终位于中心：

@IBOutlet weak var addViewConstraintX: NSLayoutConstraint!
@IBOutlet weak var addViewConstraintY: NSLayoutConstraint!
@IBOutlet weak var addView: UIView!
@IBOutlet weak var english: UITextField!
@IBOutlet weak var chinese: UITextField!

override func viewDidLoad() {
    super.viewDidLoad()
    addView.layer.cornerRadius = 10.0;
    addView.layer.masksToBounds = true;
    NotificationCenter.default.addObserver(self, selector: #selector(FirstViewController.keyboardWillShow(_:)), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
}

@objc func keyboardWillShow(_ notification:Notification) {
    print("keyboardWillShow")
}

Answer 1

您需要收听不同的通知：UIKeyboardWillChangeFrame

收到通知时，通知的userInfo字典将包含键盘的新大小。

https://developer.apple.com/documentation/uikit/uiwindow/keyboard_notification_user_info_keys

然后只需将垂直布局约束的常量更改为键盘高度的一半。

Answer 2

使用viewDidLoad方法

NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow), name: .UIKeyboardWillShow, object: nil)

其他地方

func keyboardWillShow(notification: NSNotification) {
    if let keyboardSize = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue {
        let keyboardHeight = keyboardSize.height
        addView.center = CGPoint(x: self.view.center.x, y: self.view.center.y - keyboardHeight/2)
    }
}