在swift中以编程方式从所有视图层次结构中取消键盘

import UIKit

extension UIViewController {
    func hideKeyboardWhenTappedAround() {
        let tap: UITapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(dismissKeyboard))
        tap.cancelsTouchesInView = false
        view.addGestureRecognizer(tap)
    }

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

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