How I get the keyboard frame before the keyboard appears - ios

Question

I have a button where you get a textfield with a keyboard. At the moment, when I get this textfield, the textfield is in the left corner and the textfield appears. How can I handle this, that the textfield is above my keyboard?
The problem is, that I get the keyboard height after the code in editTextButtonTapped is done. How can I get the height of the keyboard before editTextButtonTapped is called?
// This are my global Variables to create the textfield
var myTextField: UITextField = UITextField(frame: CGRect(x: 0,y: 0, width: 0, height:0))
var firstkeyboardHeight = CGFloat()
NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidShow(_:)), name: UIResponder.keyboardWillShowNotification, object: nil)
#objc func keyboardWillShow(_ notification: NSNotification) -> Void {
if let keyboardRect = (notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as AnyObject).cgRectValue {
let keyboardHeight = keyboardRect.height
firstkeyboardHeight = keyboardHeight
}
}
#IBAction func editTextButtonTapped(_ sender: UIButton) {
myTextField.becomeFirstResponder()
self.myTextField = UITextField(frame: CGRect(x: 0,y: self.firstkeyboardHeight, width: self.view.frame.width, height: 50.0))
self.myTextField.backgroundColor = .green
self.Gestures(addGesture: self.myTextField)
self.view.addSubview(self.myTextField)
}

Answer 1

There is only this set of notifications:
[ UIResponder.keyboardWillShowNotification, UIResponder.keyboardWillHideNotification, UIResponder.keyboardDidShowNotification, UIResponder.keyboardDidHideNotification]
Only inside can obtain the frame values:
NotificationCenter.default.addObserver(forName: UIResponder.keyboardWillHideNotification,
object: nil,
queue: .main) { [weak self] notification in
guard let userInfo = notification.userInfo else {
return
}
let initialValue = userInfo[UIResponder.keyboardFrameBeginUserInfoKey] as? NSValue,
let finalValue = userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue,
let durationValue = userInfo[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber,
let curveValue = userInfo[UIResponder.keyboardAnimationCurveUserInfoKey] as? NSNumber
}
So, I don't think that there are any possible allowed ways.

Answer 2

You have several ways to do that. In either case I'd avoid recreating the textfield every time.
let myTextField: UITextField = {
let textfield = UITextField()
textfield.translatesAutoresizingMaskIntoConstraints = false
textfield.backgroundColor = .green
textfield.isHidden = true
return textfield
}()
var bottomConstraint: NSLayoutConstraint?
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(myTextField)
let bottomConstraint = myTextField.bottomAnchor.constraint(equalTo: view.bottomAnchor)
NSLayoutConstraint.activate([
myTextField.leadingAnchor.constraint(equalTo: view.leadingAnchor),
myTextField.trailingAnchor.constraint(equalTo: view.trailingAnchor),
myTextField.heightAnchor.constraint(equalToConstant: 50),
bottomConstraint
])
self.bottomConstraint = bottomConstraint
NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow(_:)), name: UIResponder.keyboardWillShowNotification, object: nil)
}
#objc func keyboardWillShow(_ notification: NSNotification) -> Void {
guard let keyboardFrame = (notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue else { return }
bottomConstraint?.constant = -keyboardFrame.height
}
#IBAction func editTextButtonTapped(_ sender: UIButton) {
myTextField.becomeFirstResponder()
myTextField.isHidden = false
}