How to write Keyboard notifications in Swift 3

问题

I'm trying to update this code to swift 3:

NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillShow:"), name: UIKeyboardWillShowNotification, object: nil)

NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillHide:"), name: UIKeyboardWillHideNotification, object: nil)`

So far, I've just tried the auto corrections given by the compiler. This results in code like this:

let notificationCenter = NotificationCenter.default()
notificationCenter.addObserver(self, selector: Selector(("keyboardWillShow:")), name: NSNotification.Name.UIKeyboardWillShow, object: nil)

notificationCenter.addObserver(self, selector: Selector(("keyboardWillHide:")), name: NSNotification.Name.UIKeyboardWillHide, object: nil)`

Unfortunately, that doesn't take me far, resulting in additional errors.

Has anyone solved this please?

Please note that I'm just trying how to write the notifications. I'm not (yet) trying to fix the notification functions.. Thanks

回答1:

Swift 4

override func viewDidLoad() {
    super.viewDidLoad()   
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow), name: .UIKeyboardWillShow, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillHide), name: NSNotification.Name.UIKeyboardWillHide, object: nil)
}

func keyboardWillShow(notification: NSNotification) {
     print("keyboardWillShow")
}

func keyboardWillHide(notification: NSNotification){
     print("keyboardWillHide")
}

You Can Also Get Keyboard Info Uisng Below Code Inside These Methods.

NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillChange), name: .UIKeyboardWillChangeFrame, object: nil) .      

@objc func keyboardWillChange(notification: NSNotification) {
     let duration = notification.userInfo![UIKeyboardAnimationDurationUserInfoKey] as! Double
     let curve = notification.userInfo![UIKeyboardAnimationCurveUserInfoKey] as! UInt
     let curFrame = (notification.userInfo![UIKeyboardFrameBeginUserInfoKey] as! NSValue).cgRectValue
     let targetFrame = (notification.userInfo![UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue
     let deltaY = targetFrame.origin.y - curFrame.origin.y
 }

回答2:

Swift 4.2 Xcode 10 (10L213o)

The main changes compared with Swift 3 are in the UIWindow.keyboardWillShowNotification and UIWindow.keyboardWillHideNotification

let notifier = NotificationCenter.default
notifier.addObserver(self,
                     selector: #selector(KeyboardLayoutConstraint.keyboardWillShowNotification(_:)),
                     name: UIWindow.keyboardWillShowNotification,
                     object: nil)
notifier.addObserver(self,
                     selector: #selector(KeyboardLayoutConstraint.keyboardWillHideNotification(_:)),
                     name: UIWindow.keyboardWillHideNotification,
                     object: nil)


@objc
func keyboardWillShowNotification(_ notification: NSNotification) {}

@objc
func keyboardWillHideNotification(_ notification: NSNotification) {}

回答3:

I fixed this issue by writing the code like this

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

回答4:

For Swift 4.2 .UIKeyboardWillShow is renamed to UIResponder.keyboardWillShowNotification and .UIKeyboardWillHide is renamed to UIResponder.keyboardWillHideNotification

 NotificationCenter.default.addObserver(self, selector: #selector(NameOfSelector), name: UIResponder.keyboardWillShowNotification , object: nil)
 NotificationCenter.default.addObserver(self, selector: #selector(NameOfSelector), name: UIResponder.keyboardWillHideNotification , object: nil)

   @objc func NameOfSelector() {
       //Actions when notification is received
    }

回答5:

You can replace the deprecated string literal Selector with the type-checked #selector(Class.method) pair:

let center = NotificationCenter.default
center.addObserver(self,
                   selector: #selector(keyboardWillShow(_:)),
                   name: .UIKeyboardWillShow,
                   object: nil)

center.addObserver(self,
                   selector: #selector(keyboardWillHide(_:)),
                   name: .UIKeyboardWillHide,
                   object: nil)

The #selector syntax is much safer, since Swift is able to check at compile time that the specified method actually exists.

For more information about Swift selectors, see rickster's detailed answer.

回答6:

In Swift 3.0

 override func viewDidLoad()
    {
        super.viewDidLoad()
 NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillShow), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillHide), name: NSNotification.Name.UIKeyboardWillHide, object: nil)

}

Keybord Show and Hide

func keyboardWillShow(notification: NSNotification) 
{

      // Your Code Here
}

func keyboardWillHide(notification: NSNotification)
{  
   //Your Code Here     
}

回答7:

You can perform keyboard notification on both version of Swift respectively.

Add Objserver:

NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidShow), name: .UIKeyboardWillShow, object: nil)

Call function swift 3

func keyboardDidShow() {
          print("keyboardDidShow")
       }

Call function In swift 4

@objc func keyboardDidShow() {
      print("keyboardDidShow")
   }

回答8:

  NotificationCenter.default.addObserver(self, selector: Selector(("keyboardWillShow:")), name:UIResponder.keyboardWillShowNotification, object: nil);
    NotificationCenter.default.addObserver(self, selector: Selector(("keyboardWillHide:")), name:UIResponder.keyboardWillHideNotification, object: nil);

回答9:

Swift 5.1 + Combine + SwiftUI

@State var keyboardHeight: CGFloat = 0 // or @Published if one is in ViewModel: ObservableObject

private var cancellableSet: Set<AnyCancellable> = []

init() {

   let notificationCenter = NotificationCenter.default

   notificationCenter.publisher(for: UIWindow.keyboardWillShowNotification)
       .map {
             guard
                 let info = $0.userInfo,
                 let keyboardFrame = info[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect
                 else { return 0 }

             return keyboardFrame.height
         }
         .assign(to: \.keyboardHeight, on: self)
         .store(in: &cancellableSet)

     notificationCenter.publisher(for: UIWindow.keyboardDidHideNotification)
         .map { _ in 0 }
         .assign(to: \.keyboardHeight, on: self)
         .store(in: &cancellableSet)
    }

回答10:

Here is the best solution that works for me as far (used from "Lets Build That App" YouTube channel)

class ChatVC: UIViewController, UITableViewDelegate, UITableViewDataSource, UITextFieldDelegate {

// reference to your UIView with message TextField

    @IBOutlet weak var ChatView: UIView!   


// bottom constrain to your UIView (in my case ChatView)

    var bottomConstraint: NSLayoutConstraint?  

    override func viewDidLoad() {
        super.viewDidLoad()

// add some text in the placeholder if you want

        messageField.placeholder = "Type your message.." 

// here we add two notifications for showing and hiding the keyboard

        NotificationCenter.default.addObserver(self, selector: #selector(handleKeyboardNotification), name: UIResponder.keyboardWillShowNotification, object: nil)

        NotificationCenter.default.addObserver(self, selector: #selector(handleKeyboardNotification), name: UIResponder.keyboardWillHideNotification, object: nil)


// defines the start position for message textField that will be shown on the screen

        bottomConstraint = NSLayoutConstraint(item: ChatViewField!, attribute: .bottom, relatedBy: .equal, toItem: view, attribute: .bottom, multiplier: 1, constant: -40)    
        view.addConstraint(bottomConstraint!)    
    }

// handles notifications for both cases when keyboard pops up and disappears  

  @objc func handleKeyboardNotification(notification: NSNotification){
        if let userInfo = notification.userInfo {

            let keyboardFrame =  (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as! NSValue).cgRectValue
            print(keyboardFrame)

            let isKeyboardShowing = notification.name == UIResponder.keyboardWillShowNotification

            bottomConstraint?.constant = isKeyboardShowing ? -keyboardFrame.height : -40

// makes animation at the same time as the keyboard

UIView.animate(withDuration: 0, delay: 0, options: UIView.AnimationOptions.curveEaseOut, animations: {

                self.view.layoutIfNeeded()
            }) { (completed) in    
            }   
        }
    }

来源：https://stackoverflow.com/questions/37875973/how-to-write-keyboard-notifications-in-swift-3