Swift 3 点击屏幕任意位置隐藏键盘
func hideKeyboardWhenTappedAround() {
let tap: UITapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(UIViewController.dismissKeyboard))
tap.cancelsTouchesInView = false
view.addGestureRecognizer(tap)
}