inputAccessoryView, API error? _UIKBCompatInputView? UIViewNoIntrinsicMetric, simple code, can't figure out - ios

Question

Help me in one of the two ways maybe:
How to solve the problem? or
How to understand the error message?
Project summary
So I'm learning about inputAccessoryView by making a tiny project, which has only one UIButton. Tapping the button summons the keyboard with inputAccessoryView which contains 1 UITextField and 1 UIButton. The UITextField in the inputAccessoryView will be the final firstResponder that is responsible for the keyboard with that inputAccessoryView
The error message
API error: <_UIKBCompatInputView: 0x7fcefb418290; frame = (0 0; 0 0); layer = <CALayer: 0x60000295a5e0>> returned 0 width, assuming UIViewNoIntrinsicMetric
The code
is very straightforward as below
The custom UIView is used as inputAccessoryView. It installs 2 UI outlets, and tell responder chain that it canBecomeFirstResponder.
class CustomTextFieldView: UIView {
let doneButton:UIButton = {
let button = UIButton(type: .close)
return button
}()
let textField:UITextField = {
let textField = UITextField()
textField.placeholder = "placeholder"
return textField
}()
required init?(coder: NSCoder) {
super.init(coder: coder)
initSetup()
}
override init(frame:CGRect) {
super.init(frame: frame)
initSetup()
}
convenience init() {
self.init(frame: .zero)
}
func initSetup() {
addSubview(doneButton)
addSubview(textField)
}
func autosizing(to vc: UIViewController) {
frame = CGRect(x: 0, y: 0, width: vc.view.frame.size.width, height: 40)
let totalWidth = frame.size.width - 40
doneButton.frame = CGRect(x: totalWidth * 4 / 5 + 20,
y: 0,
width: totalWidth / 5,
height: frame.size.height)
textField.frame = CGRect(x: 20,
y: 0,
width: totalWidth * 4 / 5,
height: frame.size.height)
}
override var canBecomeFirstResponder: Bool { true }
override var intrinsicContentSize: CGSize {
CGSize(width: 400, height: 40)
} // overriding this variable seems to have no effect.
}
Main VC uses the custom UIView as inputAccessoryView. The UITextField in the inputAccessoryView becomes the real firstResponder in the end, I believe.
class ViewController: UIViewController {
let customView = CustomTextFieldView()
var keyboardShown = false
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
customView.autosizing(to: self)
}
#IBAction func summonKeyboard() {
print("hello")
keyboardShown = true
self.becomeFirstResponder()
customView.textField.becomeFirstResponder()
}
override var canBecomeFirstResponder: Bool { keyboardShown }
override var inputAccessoryView: UIView? {
return customView
}
}
I've seen people on the internet says this error message will go away if I run on a physical phone. I didn't go away when I tried.
I override intrinsicContentSize of the custom view, but it has no effect.
The error message shows twice together when I tap summon.
What "frame" or "layer" does the error message refer to? Does it refer to the custom view's frame and layer?

Answer 1

If we use Debug View Hierarchy we can see that _UIKBCompatInputView is part of the (internal) view hierarchy of the keyboard.
It's not unusual to see constraint errors / warnings with internal views.
Since frame and/or intrinsic content size seem to have no effect, I don't think it can be avoided (nor does it seem to need to be).
As a side note, you can keep the "Done" button round by using auto-layout constraints. Here's an example:
class CustomTextFieldView: UIView {
let textField: UITextField = {
let tf = UITextField()
tf.font = .systemFont(ofSize: 16)
tf.autocorrectionType = .no
tf.returnKeyType = .done
tf.placeholder = "placeholder"
// textField backgroundColor so we can see its frame
tf.backgroundColor = .yellow
return tf
}()
let doneButton:UIButton = {
let button = UIButton(type: .close)
return button
}()
override init(frame: CGRect) {
super.init(frame: frame)
commonInit()
}
required init?(coder: NSCoder) {
super.init(coder: coder)
commonInit()
}
func commonInit() -> Void {
autoresizingMask = [.flexibleHeight, .flexibleWidth]
[doneButton, textField].forEach { v in
v.translatesAutoresizingMaskIntoConstraints = false
addSubview(v)
}
NSLayoutConstraint.activate([
// constrain doneButton
// Trailing: 20-pts from trailing
doneButton.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -20.0),
// Top and Bottom 8-pts from top and bottom
doneButton.topAnchor.constraint(equalTo: topAnchor, constant: 8.0),
doneButton.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -8.0),
// Width equal to default height
// this will keep the button round instead of oval
doneButton.widthAnchor.constraint(equalTo: doneButton.heightAnchor),
// constrain textField
// Leading: 20-pts from leading
textField.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 20.0),
// Trailing: 8-pts from doneButton leading
textField.trailingAnchor.constraint(equalTo: doneButton.leadingAnchor, constant: -8.0),
// vertically centered
textField.centerYAnchor.constraint(equalTo: centerYAnchor),
])
}
}
class CustomTextFieldViewController: UIViewController {
let customView = CustomTextFieldView()
var keyboardShown = false
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func summonKeyboard() {
print("hello")
keyboardShown = true
self.becomeFirstResponder()
customView.textField.becomeFirstResponder()
}
override var canBecomeFirstResponder: Bool { keyboardShown }
override var inputAccessoryView: UIView? {
return customView
}
}