iOS 开发之路（登陆页键盘遮挡输入框问题）一

@IBOutlet weak var bottomConstraint: NSLayoutConstraint!    //注意这里要在storyboard对最底部的控件设置约束，然后连线到.swift文件进行绑定
　　override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default.addObserver(self, selector:#selector(keyboardWillChange(notification:)),  
             name: NSNotification.Name.UIKeyboardWillChangeFrame, object: nil)
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        self.view.endEditing(true)
    }

    // 键盘改变
    func keyboardWillChange(notification: NSNotification) {
        if let userInfo = notification.userInfo,
            let value = userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue,
            let duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? Double,
            let curve = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? UInt {
            
            let frame = value.cgRectValue
            
            var intersection = frame.intersection(self.view.frame)
            //当键盘消失，让view回归原始位置
            if intersection.height == 0.0 {
                intersection = CGRect(x: intersection.origin.x, y: intersection.origin.y, width: intersection.width, height: 100)
            }
            UIView.animate(withDuration: duration, delay: 0.0,
                                       options: UIViewAnimationOptions(rawValue: curve), animations: {
                                        _ in
                                        //改变下约束
                                        self.bottomConstraint.constant = intersection.height
                                        self.view.layoutIfNeeded()
            }, completion: nil)
        }
    }