How to detect when keyboard is shown and hidden
You may just need addObserver
in viewDidLoad
. But having addObserver
in viewWillAppear
and removeObserver
in viewWillDisappear
prevents rare crashes which happens when you are changing your view.
Swift 4.2
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillDisappear), name: UIResponder.keyboardWillHideNotification, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillAppear), name: UIResponder.keyboardWillShowNotification, object: nil)
}
@objc func keyboardWillAppear() {
//Do something here
}
@objc func keyboardWillDisappear() {
//Do something here
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
NotificationCenter.default.removeObserver(self)
}
Swift 3 and 4
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillDisappear), name: Notification.Name.UIKeyboardWillHide, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillAppear), name: Notification.Name.UIKeyboardWillShow, object: nil)
}
@objc func keyboardWillAppear() {
//Do something here
}
@objc func keyboardWillDisappear() {
//Do something here
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
NotificationCenter.default.removeObserver(self)
}
Older Swift
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
NSNotificationCenter.defaultCenter().addObserver(self, selector:"keyboardWillAppear:", name: UIKeyboardWillShowNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector:"keyboardWillDisappear:", name: UIKeyboardWillHideNotification, object: nil)
}
func keyboardWillAppear(notification: NSNotification){
// Do something here
}
func keyboardWillDisappear(notification: NSNotification){
// Do something here
}
override func viewWillDisappear(animated: Bool) {
super.viewWillDisappear(animated)
NSNotificationCenter.defaultCenter().removeObserver(self)
}
Swift 5
There answers above are correct. Although I would prefer to create a helper to wrap up the notification's observers
.
The benefit:
- You don't have to repeat each time you handle the keyboard behaviors.
- You can extend other notification by implement other enum value
- It's useful when you have to deal with keyboard in several controllers.
Sample code:
extension KeyboardHelper {
enum Animation {
case keyboardWillShow
case keyboardWillHide
}
typealias HandleBlock = (_ animation: Animation, _ keyboardFrame: CGRect, _ duration: TimeInterval) -> Void
}
final class KeyboardHelper {
private let handleBlock: HandleBlock
init(handleBlock: @escaping HandleBlock) {
self.handleBlock = handleBlock
setupNotification()
}
deinit {
NotificationCenter.default.removeObserver(self)
}
private func setupNotification() {
_ = NotificationCenter.default
.addObserver(forName: UIResponder.keyboardWillShowNotification, object: nil, queue: .main) { [weak self] notification in
self?.handle(animation: .keyboardWillShow, notification: notification)
}
_ = NotificationCenter.default
.addObserver(forName: UIResponder.keyboardWillHideNotification, object: nil, queue: .main) { [weak self] notification in
self?.handle(animation: .keyboardWillHide, notification: notification)
}
}
private func handle(animation: Animation, notification: Notification) {
guard let userInfo = notification.userInfo,
let keyboardFrame = (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue,
let duration = userInfo[UIResponder.keyboardAnimationDurationUserInfoKey] as? Double
else { return }
handleBlock(animation, keyboardFrame, duration)
}
}
How to use:
private var keyboardHelper: KeyboardHelper?
...
override func viewDidLoad() {
...
keyboardHelper = KeyboardHelper { [unowned self] animation, keyboardFrame, duration in
switch animation {
case .keyboardWillShow:
print("keyboard will show")
case .keyboardWillHide:
print("keyboard will hide")
}
}
}
In the ViewDidLoad method of your class set up to listen for messages about the keyboard:
// Listen for keyboard appearances and disappearances
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(keyboardDidShow:)
name:UIKeyboardDidShowNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(keyboardDidHide:)
name:UIKeyboardDidHideNotification
object:nil];
Then in the methods you specify (in this case keyboardDidShow
and keyboardDidHide
) you can do something about it:
- (void)keyboardDidShow: (NSNotification *) notif{
// Do something here
}
- (void)keyboardDidHide: (NSNotification *) notif{
// Do something here
}
Swift 3:
NotificationCenter.default.addObserver(self, selector: #selector(viewController.keyboardWillShow(_:)), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(viewController.keyboardWillHide(_:)), name: NSNotification.Name.UIKeyboardWillHide, object: nil)
func keyboardWillShow(_ notification: NSNotification){
// Do something here
}
func keyboardWillHide(_ notification: NSNotification){
// Do something here
}