UIKeyboardWillShow notification called twice on physical device but not in simulator - ios

Question

I'm moving a UIView up when the keyboard is called, works fine in the simulator but when i run the code on an actual device for whatever reason the UIKeyboardWillShow notification is called twice. I am not using any custom keyboards.
In the viewDidLoad method i call this method.
func registerKeyBoardNotifications(){
NotificationCenter.default.addObserver(self, selector: #selector(keyBoardWillAppear(notification:)), name: .UIKeyboardWillShow, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillBeHidden(notification:)), name: .UIKeyboardWillHide, object: nil)
}
Then remove these observers in viewWillDisappear.
#objc func keyBoardWillAppear(notification: NSNotification){
if let userInfo = notification.userInfo,
let endFrame = userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue,
let beginFrame = userInfo[UIKeyboardFrameBeginUserInfoKey] as? NSValue,
beginFrame.isEqual(to: endFrame) == false{
let keyboardSize = endFrame.cgRectValue
self.view.frame.origin.y -= keyboardSize.height - keyboardConstant
signUpButton.isEnabled = false
}
}
the keyboardWillAppear handler is called twice on a physical device but once in the simulator, spent the last 2 days trying to figure this out.
Xcode 9.4.1 swift 4.1

Answer 1

This can happen and there is no documentation that guarantees just one notification.
So you should just deal with it in your code and not substract the keyboard height every time. A smarter solution would be to calculate your view frame depending on keyboard's end frame.

Answer 2

The right approach, as you've been told, is to ask yourself the right question. For example, is it the case that previously the keyboard was not covering my view, but now it is? That is the occasion that should be regarded as "entering".
I have a utility function that works out the geometry based on the notification's userInfo dictionary and the bounds of the view we're concerned with. If the keyboard wasn't within the view's bounds and now it will be, it is entering; if it was within the view's bounds and now it won't be, it is exiting. We return that information, along with the keyboard's frame in the view's bounds coordinates:
enum KeyboardState {
case unknown
case entering
case exiting
}
func keyboardState(for d:[AnyHashable:Any], in v:UIView?)
-> (KeyboardState, CGRect?) {
var rold = d[UIResponder.keyboardFrameBeginUserInfoKey] as! CGRect
var rnew = d[UIResponder.keyboardFrameEndUserInfoKey] as! CGRect
var ks : KeyboardState = .unknown
var newRect : CGRect? = nil
if let v = v {
let co = UIScreen.main.coordinateSpace
rold = co.convert(rold, to:v)
rnew = co.convert(rnew, to:v)
newRect = rnew
if !rold.intersects(v.bounds) && rnew.intersects(v.bounds) {
ks = .entering
}
if rold.intersects(v.bounds) && !rnew.intersects(v.bounds) {
ks = .exiting
}
}
return (ks, newRect)
}
When the keyboard shows, we check whether it is entering, and respond accordingly:
#objc func keyboardShow(_ n:Notification) {
let d = n.userInfo!
let (state, rnew) = keyboardState(for:d, in:myView)
if state == .entering {
// ...
}
}

Answer 3

i seem to have figured out why the UIkeyboardWillShow Notification fires twice on the physical device and not the simulator. It has to do with the keyboard suggestions above the keyboard when you set certain Text Input traits. Any text input trait that causes a suggestion above the keyboard will cause the notification to fire twice instead of once, i'm guessing once for the keyboard itself and again for the suggestion bar above the keyboard. (in my case because there were no suggestions on the simulator it fired once in the simulator, but fired twice on the device because there were suggestions on a real device). This is a weird case thing that doesn't seem to be documented.
One way to deal with this (the route i chose) is to disable all suggestions by setting all Text Input traits to default and the content type of the text field to Username.
The other solution is to account for the second UIkeyboardWillShowNotifcation notification in your code before adjusting the frame of the UIView you're trying move.