通知方法，获取键盘的左上角的point值，方便之后做其他的操作。
NotificationCenter.default.addObserver(self, selector: #selector(keyBoardWillShow), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(keyBoardWillHide), name: NSNotification.Name.UIKeyboardWillHide, object: nil)
// 当键盘弹出时调用的方法
func keyBoardWillShow(_ notification:Notification){
let dict = NSDictionary(dictionary: notification.userInfo!)
let keyBoardFrame = (dict[UIKeyboardFrameEndUserInfoKey]! asAnyObject).cgRectValue
let point = keyBoardFrame?.origin
self.frame = CGRect(x: (point?.x)!, y: (point?.y)! - mViewHeight, width: mWidth, height: mViewHeight)
}
func keyBoardWillHide(_ notification: Notification) {
self.frame = CGRect(x: 0, y: mHeight - mViewHeight, width: mWidth, height: mViewHeight)
}
