我没有看到它被提到过，但是NotificationCenter可以告诉你键盘何时打开和关闭。例如，如果你想改变cancelsTouchesInView或一起删除手势识别器，这可以被使用。

例子:

var dismissKeyboardGestureRecognizer = UITapGestureRecognizer()

override func viewDidLoad() {
    super.viewDidLoad()

    //Setup dismiss keyboard gesture
    self.dismissKeyboardGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(dismissKeyboard))

    //Add Notifications
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidShow), name:UIResponder.keyboardDidShowNotification, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidHide), name:UIResponder.keyboardDidHideNotification, object: nil)
}

@objc func keyboardDidShow() {
    dismissKeyboardGestureRecognizer.cancelsTouchesInView = true
    view.addGestureRecognizer(dismissKeyboardGestureRecognizer)
}

@objc func keyboardDidHide() {
    dismissKeyboardGestureRecognizer.cancelsTouchesInView = false
    view.removeGestureRecognizer(dismissKeyboardGestureRecognizer)
}

@objc func dismissKeyboard() {
    view.endEditing(true)
}

添加这个扩展到你的ViewController:

  extension UIViewController {
// Ends editing view when touches to view 
  open override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesBegan(touches, with: event)
    self.view.endEditing(true)
  }
}

override func viewDidLoad() {
    super.viewDidLoad()
          
    //Looks for single or multiple taps. 
     let tap = UITapGestureRecognizer(target: self, action: #selector(UIInputViewController.dismissKeyboard))

    //Uncomment the line below if you want the tap not not interfere and cancel other interactions.
    //tap.cancelsTouchesInView = false 

    view.addGestureRecognizer(tap)
}

//Calls this function when the tap is recognized.
@objc func dismissKeyboard() {
    //Causes the view (or one of its embedded text fields) to resign the first responder status.
    view.endEditing(true)
}

如果你打算在多个uiviewcontroller中使用这个功能，这里有另一种方法来完成这个任务:

// Put this piece of code anywhere you like
extension UIViewController {
    func hideKeyboardWhenTappedAround() {
        let tap = UITapGestureRecognizer(target: self, action: #selector(UIViewController.dismissKeyboard))
        tap.cancelsTouchesInView = false            
        view.addGestureRecognizer(tap)
    }
    
    @objc func dismissKeyboard() {
        view.endEditing(true)
    }
}

现在在每个UIViewController中，你要做的就是调用这个函数:

override func viewDidLoad() {
    super.viewDidLoad()
    self.hideKeyboardWhenTappedAround() 
}

这个函数是我的repo中包含的标准函数，它包含了很多有用的Swift扩展，比如这个，看看:https://github.com/goktugyil/EZSwiftExtensions

如果你有其他视图也应该接收触摸，你必须设置 cancelsTouchesInView = false

是这样的:

let elsewhereTap = UITapGestureRecognizer(target: self, action: #selector(dismissKeyboard))
    elsewhereTap.cancelsTouchesInView = false
    self.view.addGestureRecognizer(elsewhereTap)

//Simple exercise to demonstrate, assuming the view controller has a //Textfield, Button and a Label. And that the label should display the //userinputs when button clicked. And if you want the keyboard to disappear //when clicken anywhere on the screen + upon clicking Return key in the //keyboard. Dont forget to add "UITextFieldDelegate" and 
//"self.userInput.delegate = self" as below

import UIKit

class ViewController: UIViewController,UITextFieldDelegate {

    @IBOutlet weak var userInput: UITextField!
    @IBAction func transferBtn(sender: AnyObject) {
                display.text = userInput.text

    }
    @IBOutlet weak var display: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

//This is important for the textFieldShouldReturn function, conforming to textfieldDelegate and setting it to self
        self.userInput.delegate = self
    }

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

//This is for the keyboard to GO AWAYY !! when user clicks anywhere on the view
    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        self.view.endEditing(true)
    }


//This is for the keyboard to GO AWAYY !! when user clicks "Return" key  on the keyboard

    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        return true
    }

}

我找到了一个简单的解决办法: 1. 添加UITapGestureRecognizer到你的视图控制器 2. 添加IBAction到你的UITapGestureRecognizer 3.最后，您可以放弃第一个响应器

class ViewController: UIViewController
{

@IBOutlet var tap: UITapGestureRecognizer!
@IBOutlet weak var label: UILabel!
@IBOutlet weak var textField: UITextField!
override func viewDidLoad()
{
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}


@IBAction func dismissUsingGesture(_ sender: UITapGestureRecognizer)
{
   self.textField.resignFirstResponder()
    label.text = textField.text!
}
}