override func viewDidLoad() {
    super.viewDidLoad()

    //Looks for single or multiple taps. 
    let tap: UITapGestureRecognizer = UITapGestureRecognizer(target: self,action: "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.
func dismissKeyboard() {
    //Causes the view (or one of its embedded text fields) to resign the first responder status.
    view.endEditing(true)
}

================================================== ======================

编辑：如果要在多个UIViewControllers中使用此功能，这里是另一种方法来执行此任务：

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

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

现在在每个UIViewController，所有你要做的是调用此函数：

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

这个函数作为一个标准函数包含在我的仓库，其中包含了很多有用的Swift扩展，像这样，检查：https://github.com/goktugyil/EZSwiftExtensions