出现键盘时更改约束-Swift

Question

键盘出现时，我的UIView不能正常移动。我用来输入文本的UIView中有一个UITextView。如果我选择TextView输入文本，则会出现键盘，但UIView不会第一次移动。如果我点击背景并使键盘消失，然后再次点击TextView，则UIView会正确向上移动。有人知道这里发生了什么吗？

class ChatViewController: UIViewController, CNContactPickerDelegate, UISearchBarDelegate, UITableViewDelegate, UITableViewDataSource, UIToolbarDelegate, UITextFieldDelegate, UITextViewDelegate {

@IBOutlet weak var composeTextView: UITextView!

@IBOutlet weak var composeViewBottomConstraint: NSLayoutConstraint!

override func viewDidLoad() {
    super.viewDidLoad()

    composeTextView.delegate = self

}

func textViewDidBeginEditing(_ textView: UITextView) {

    UIView.animate(withDuration: 0.5){
        NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillShow), name: .UIKeyboardWillShow, object: nil)

    }

    self.view.layoutIfNeeded()


}

@objc func keyboardWillShow(notification: Notification) {
    let keyboardSize = (notification.userInfo?[UIKeyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue

    let keyboardHeight = keyboardSize?.height

        if #available(iOS 11.0, *){

            self.composeViewBottomConstraint.constant = keyboardHeight! - view.safeAreaInsets.bottom
        }
        else {
            self.composeViewBottomConstraint.constant = view.safeAreaInsets.bottom
        }
        self.view.layoutIfNeeded()

}

}

Answer 1

问题在于，在第一次单击textView时视图没有上升，是在beginEditing中添加了showKeyboard观察器，因此该行应位于 viewDidLoad

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

除了以下修复程序

func textViewDidBeginEditing(_ textView: UITextView) {

     // I think no need for it

}

 @objc func keyboardWillShow(notification: Notification) {

     let keyboardSize = (notification.userInfo?  [UIKeyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue

     let keyboardHeight = keyboardSize?.height

     if #available(iOS 11.0, *){

          self.composeViewBottomConstraint.constant = keyboardHeight! - view.safeAreaInsets.bottom
      }
      else {
           self.composeViewBottomConstraint.constant = view.safeAreaInsets.bottom
         }

       UIView.animate(withDuration: 0.5){

          self.view.layoutIfNeeded()

       }


   }

  @objc func keyboardWillHide(notification: Notification){

      self.composeViewBottomConstraint.constant =  0 // or change according to your logic  

       UIView.animate(withDuration: 0.5){

          self.view.layoutIfNeeded()

       }

  }