Swift让输入框跟随键盘弹起避免输入输入法挡住输入框问题

//当键盘弹起的时候会向系统发出一个通知，
//这个时候需要注册一个监听器响应该通知
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(LoginViewController.keyboardWillShow(_:)), name:UIKeyboardWillShowNotification, object: nil)
//当键盘收起的时候会向系统发出一个通知，
//这个时候需要注册另外一个监听器响应该通知
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(LoginViewController.keyboardWillHide(_:)), name:UIKeyboardWillHideNotification, object: nil)

var keyBoardNeedLayout: Bool = true

func keyboardWillShow(notification: NSNotification) {
print("show")
if let userInfo = notification.userInfo,
value = userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue,
duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? Double,
curve = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? UInt {
let frame = value.CGRectValue()
let intersection = CGRectIntersection(frame, self.view.frame)
let deltaY = CGRectGetHeight(intersection)
if keyBoardNeedLayout {
UIView.animateWithDuration(duration, delay: 0.0,
options: UIViewAnimationOptions(rawValue: curve),
animations: { _ in
self.view.frame = CGRectMake(0,-deltaY,self.view.bounds.width,self.view.bounds.height)
self.keyBoardNeedLayout = false
self.view.layoutIfNeeded()
}, completion: nil)
}
}
}

func keyboardWillHide(notification: NSNotification) {
print("hide")
if let userInfo = notification.userInfo,
value = userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue,
duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? Double,
curve = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? UInt {
let frame = value.CGRectValue()
let intersection = CGRectIntersection(frame, self.view.frame)
let deltaY = CGRectGetHeight(intersection)
UIView.animateWithDuration(duration, delay: 0.0,
options: UIViewAnimationOptions(rawValue: curve),
animations: { _ in
self.view.frame = CGRectMake(0,deltaY,self.view.bounds.width,self.view.bounds.height)
self.keyBoardNeedLayout = true
self.view.layoutIfNeeded()
}, completion: nil)
}
}

self.view.frame = CGRectMake(0,-deltaY,self.view.bounds.width,self.view.bounds.height)