toolBarView.snp.makeConstraints { (make) in
 make.left.equalTo(view.snp.left)
 make.right.equalTo(view.snp.right)
 make.height.equalTo(toolBarHeight)
 make.bottom.equalTo(view.snp.bottom)
}

chatTableView.snp.makeConstraints { (make) in
 make.left.equalTo(view.snp.left)
 make.right.equalTo(view.snp.right)
 make.bottom.equalTo(toolBarView.snp.top)
 make.top.equalTo(view.snp.top).offset(64)
}

NotificationCenter.default.addObserver(self, 
selector: #selector(keyBoardWillShow(notification:)), name: NSNotification.Name.UIKeyboardWillShow, 
object: nil)

NotificationCenter.default.addObserver(self, 
selector: #selector(keyBoardWillHide(notification:)), name: NSNotification.Name.UIKeyboardWillHide, 
object: nil)

func keyBoardWillShow(notification: Notification) {
 let userInfo = notification.userInfo! as Dictionary
 let value = userInfo[UIKeyboardFrameEndUserInfoKey] as! NSValue
 let keyBoardRect = value.cgRectValue
 // 得到键盘高度
 let keyBoardHeight = keyBoardRect.size.height
 mKeyBoardHeight = keyBoardHeight

 // 得到键盘弹出所需时间
 let duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as! NSNumber
 mKeyBoardAnimateDuration = duration.doubleValue

 ...
}

var animate: (()->Void) = {
 let newFrame = CGRect(x: 0, y: 0, width: SCREEN_WIDTH, height: SCREEN_HEIGHT - mKeyBoardHeight)
 self.toolBarView.frame = newFrame
}

UIView.animate(withDuration: mKeyBoardAnimateDuration,
 delay: 0, options: options, animations: animate)

var animate: (()->Void) = {
 self.toolBarView.snp.updateConstraints(closure: { (make) in
 make.bottom.equalTo(self.view.snp_bottom).offset(-mKeyBoardHeight) 
 }
}

UIView.animate(withDuration: mKeyBoardAnimateDuration,
 delay: 0, options: options, animations: animate)

var animate: (()->Void) = {
 self.toolBarView.transform = CGAffineTransform(translationX: 0, y: -keyBoardHeight)
}

let options = UIViewAnimationOptions(rawValue: 
UInt((userInfo[UIKeyboardAnimationCurveUserInfoKey] 
as! NSNumber).intValue << 16))

UIView.animate(withDuration: mKeyBoardAnimateDuration,
 delay: 0, options: options, animations: animate)

enum AnimateType {
 case animate1 // 键盘弹出的话不会遮挡消息
 case animate2 // 键盘弹出的话会遮挡消息，但最后一条消息距离输入框有一段距离
 case animate3 // 最后一条消息距离输入框在小范围内，这里设为 30
}

var animate: (()->Void) = {
 self.toolBarView.transform = CGAffineTransform(translationX: 0, y: -keyBoardHeight)
}

let lastIndex = IndexPath(row: msgList.count - 1, section: 0)
let rectCellView = chatTableView.rectForRow(at: lastIndex)
let rect = chatTableView.convert(rectCellView, to: chatTableView.superview)
let cellDistance = rect.origin.y + rect.height

let distance1 = SCREEN_HEIGHT - toolBarHeight - keyBoardHeight
let distance2 = SCREEN_HEIGHT - toolBarHeight - 2 * fitBlank

let difY = cellDistance - distance1

if cellDistance <= distance1 {
 animate = {
  self.toolBarView.transform = CGAffineTransform(translationX: 0, y: -keyBoardHeight)
 }
 animateType = .animate1
} else if distance1 < cellDistance && cellDistance <= distance2 {
 animate = {
  self.toolBarView.transform = CGAffineTransform(translationX: 0, y: -keyBoardHeight)
  self.chatTableView.transform = CGAffineTransform(translationX: 0, y: -difY)
  self.lastDifY = difY //这里记录下最后一次滑动的dif值，以后有用
 }
 animateType = .animate2
} else {
 animate = {
  self.view.transform = CGAffineTransform(translationX: 0, y: -keyBoardHeight)
 }
 animateType = .animate3
}

// 返回 view 或 toolBarView 或 chatTableView 到原有状态
switch animateType {
case .animate1:
 animate = {
 self.toolBarView.transform = CGAffineTransform.identity
 self.chatTableView.transform = CGAffineTransform.identity
 }
case .animate2:
 animate = {
 self.toolBarView.transform = CGAffineTransform.identity
 self.chatTableView.transform = CGAffineTransform.identity
 }
case .animate3:
 animate = {
 self.view.transform = CGAffineTransform.identity
 }
}

// 刷新列表
 func reloadTableView() {
 chatTableView.reloadData()
 chatTableView.layoutIfNeeded()

 // 得到最后一条消息在view中的位置
 let lastIndex = IndexPath(row: msgList.count - 1, section: 0)
 let rectCellView = chatTableView.rectForRow(at: lastIndex)
 let rect = chatTableView.convert(rectCellView, to: chatTableView.superview)
 let cellDistance = rect.origin.y + rect.height
 let distance1 = SCREEN_HEIGHT - toolBarHeight - mKeyBoardHeight

 // 计算键盘可能遮住的消息的长度
 let difY = cellDistance - distance1


 if animateType == .animate3 {
  // 处于情况三时，由于之前的约束（聊天界面在输入栏上方），并且
  // 是整个界面一起上滑，所以约束依旧成立，只需把聊天界面最后
  // 一条消息滚动到聊天界面底部即可
  scrollToBottom()
 } else if (animateType == .animate1 || animateType == .animate2) && difY > 0{
  // 在情况一和情况二中，如果聊天界面上滑的总距离小于键盘高度，则可以继续上滑
  // 一旦聊天界面上滑的总距离 lastDifY + difY 将要超过键盘高度，则上滑总距离设为键盘高度
  // 此时执行 trans 动画
  // 一旦聊天界面上滑总距离为键盘高度，则变为情况三的情况，把聊天界面最后
  // 一条消息滚动到聊天界面底部即可
  if lastDifY + difY < mKeyBoardHeight {
  lastDifY += difY
  let animate: (()->Void) = {
   self.chatTableView.transform = CGAffineTransform(translationX: 0, y: -self.lastDifY)
  }
  UIView.animate(withDuration: mKeyBoardAnimateDuration, delay: 0, options: animateOption, animations: animate)

  } else if lastDifY + difY > mKeyBoardHeight {
  if lastDifY != mKeyBoardHeight {
   let animate: (()->Void) = {
   self.chatTableView.transform = CGAffineTransform(translationX: 0, y: -self.mKeyBoardHeight)
   }
   UIView.animate(withDuration: mKeyBoardAnimateDuration, delay: 0, options: animateOption, animations: animate)
   lastDifY = mKeyBoardHeight
  }
  scrollToBottom()
  }
 }

 }

func scrollToBottom() {
 if msgList.count > 0 {
 chatTableView.scrollToRow(at: IndexPath(row: msgList.count - 1, section: 0), at: .bottom, animated: true)
 }
}