NotificationCenter: Toggling keyboard multiple times sets y-position to weird value

问题

I've got a UIViewController with a UITableView. I'm using NotificationCenter to set the y-coordinates for the view to adjust when the keyboard shows and hides again. For the first show + hide, everything looks fine. Doing it a second time messes up things on the screen. I've included print statements in the show / hide actions to get to the bottom of it - see below.

class ChatDetailViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

    @IBOutlet weak var UserLogo: UIImageView!
    @IBOutlet weak var UserName: UILabel!
    @IBOutlet weak var MessageList: UITableView!
    var conversation: Int = 0
    let apiService = APIService()
    var conversationDetails: ConversationDetails?



    override func viewDidLoad() {
        super.viewDidLoad()

        self.UserName.text = ""
        self.MessageList.separatorStyle = .none
        self.MessageList.delegate = self
        self.MessageList.dataSource = self

        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow), name: UIResponder.keyboardWillShowNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide), name: UIResponder.keyboardWillHideNotification, object: nil)
// https://stackoverflow.com/questions/59773010/app-crashing-exception-unrecognised-selector-sent-to-instance

        // load messages:
        self.apiService.getChatMessages(conversation: self.conversation, completion: {result in
            switch result {
            case .success(let conversationDetails):
                DispatchQueue.main.async {
                    self.conversationDetails = conversationDetails
                    // prepare header section:
                    let URLstring = self.conversationDetails?.participants![0].profileimage
                    let imgURL = URL(string: URLstring ?? "www.foo.com") // TODO: insert placeholder image
                    self.UserLogo.sd_setImage(with: imgURL, placeholderImage: UIImage(named: "icon.turq.png"))
                    self.UserLogo.clipsToBounds = true
                    self.UserLogo.layer.cornerRadius = self.UserLogo.frame.size.width / 2
                    self.UserName.text = self.conversationDetails?.participants![0].username
                    self.MessageList.reloadData()
                }
            case .failure(let error):
                print("An error occured \(error.localizedDescription)")
            }
        })
    }



    @objc func keyboardWillShow(_ notification: Notification) {
        if let keyboardSize = (notification.userInfo?[UIResponder.keyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue {
            print(self.view)
            print("pre-show: ",view.frame.origin.y)
            self.view.frame.origin.y -= keyboardSize.height
            print("post-show:",view.frame.origin.y)
        }
    }

    @objc func keyboardWillHide(_ notification: Notification) {
        print("pre-hide: ",view.frame.origin.y)
        self.view.frame.origin.y = 0.0
        print("post-hide:",view.frame.origin.y)
    }

...

}

This is the console output for a single show / hide iteration:

Optional(<UIView: 0x7fd6d6522d40; frame = (0 0; 375 758); autoresize = W+H; layer = <CALayer: 0x600000a900c0>>)
pre-show:  0.0
post-show: -278.0
Optional(<UIView: 0x7fd6d6522d40; frame = (0 -278; 375 758); autoresize = W+H; layer = <CALayer: 0x600000a900c0>>)
pre-show:  -278.0
post-show: -614.0
pre-hide:  -614.0
post-hide: 0.0

And this is what is shown after the second iteration:

Optional(<UIView: 0x7fd6d6522d40; frame = (0 0; 375 758); autoresize = W+H; layer = <CALayer: 0x600000a900c0>>)
pre-show:  0.0
post-show: -69.0
Optional(<UIView: 0x7fd6d6522d40; frame = (0 -69; 375 758); autoresize = W+H; layer = <CALayer: 0x600000a900c0>>)
pre-show:  -69.0
post-show: -405.0
pre-hide:  -405.0
post-hide: 0.0

I don't understand why 1) according to the console output, keyboardWillShow seems to also get called when the keyboard slides down again - so twice per single cycle instead of 1 x show and 1 x hide 2) post-show has a different value in the second iteration - i.e. -69.0 instead of -278.0

Can someone help me to understand what's going wrong here?

来源：https://stackoverflow.com/questions/59789728/notificationcenter-toggling-keyboard-multiple-times-sets-y-position-to-weird-va

标签

swift

notificationcenter