//MARK:監(jiān)聽鍵盤通知
 func registerNotification(){
  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)
 }

 //MARK:鍵盤通知相關(guān)操作
 @objc func keyBoardWillShow(_ notification:Notification){

  DispatchQueue.main.async {
   /*
    每次鍵盤發(fā)生變化之前，先恢復(fù)原來的狀態(tài)
    y 是鍵盤布局的origin.y
    y2 是登錄按鈕的origin.y+height
    如果y>y2，登錄按鈕沒有被遮擋，不需要向上移動(dòng)；反之，按鈕被遮擋，整體需要向上移動(dòng)一部分
    */
   self.view.center = CGPoint.init(x: Width/2, y: Height/2)
   let user_info = notification.userInfo
   let keyboardRect = (user_info?[UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue
   let y = keyboardRect.origin.y
   let y2 = (self.nextStep?.frame.origin.y)! + (self.nextStep?.frame.size.height)! + 5
   let offset_y = y2 > y ? (y2-y):(0)
   UIView.animate(withDuration: 0.25, animations: {
    self.view.center = CGPoint.init(x: Width/2, y: self.view.center.y - offset_y)
   })
  }
 }

 @objc func keyBoardWillHide(_ notification:Notification){
  DispatchQueue.main.async {
   self.view.center = CGPoint.init(x: Width/2, y: Height/2)
  }
 }

//MARK:釋放鍵盤監(jiān)聽通知
 func releaseNotification(){
  NotificationCenter.default.removeObserver(self)
 }