使用 iOS11 Simulator 调用两次键盘显示通知

Question

我正在使用UIKeyboardFrameEndUserInfoKey 键获取键盘高度，如下所示：

let keyboardHeight = (userInfo[UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue.height
print(keyboardHeight)

如果我点击UITextView，键盘会出现并打印

258.0

然后我按⌘ + k，模拟器连接硬件键盘，因此模拟器上的软件键盘关闭。

如果我按⌘ + k 再次启动键盘，keyboardShow 通知会调用两次并打印

216.0
258.0

为什么键盘显示通知会被调用两次，为什么是216.0？

更新

这是我的整个代码。

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let notificationCenter = NotificationCenter.default
        notificationCenter.addObserver(self, selector: #selector(ViewController.keyboardWillShow(notification:)), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
        notificationCenter.addObserver(self, selector: #selector(ViewController.keyboardWillHide(notification:)), name: NSNotification.Name.UIKeyboardWillHide, object: nil)
    }

    @objc func keyboardWillShow(notification: NSNotification) {
        let userInfo = notification.userInfo!
        let keyboardHeight = (userInfo[UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue.height

        print(keyboardHeight);
    }

    @objc func keyboardWillHide(notification: NSNotification) {

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

如果我多次按⌘ + k 会显示结果...

result console image

Answer 1

不确定您是如何声明 observer 的，但以下内容在 Xcode 8 和 Xcode 9 beta (iOS 11) 中都可以正常工作。

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

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

@objc func keyboardWillShow(sender: NSNotification) {
    let keyboardHeight = (sender.userInfo?[UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue.height
    print(keyboardHeight)
}

更新：
刚刚测试了你的代码，它符合要求并且工作正常，你一定有其他东西在干扰它。

测试后的输出：
226.0
226.0
226.0
226.0
226.0
226.0