键盘通知

** 即将出现 发送通知**

-(void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear:animated];
    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(openKeyboard:) name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(closeKeyboard:) name:UIKeyboardWillHideNotification object:nil];
}```
** 即将消失,销毁通知**

-(void)viewWillDisappear:(BOOL)animated{
[super viewWillDisappear:animated];
[[NSNotificationCenter defaultCenter]removeObserver:self name:UIKeyboardWillShowNotification object:nil];
[[NSNotificationCenter defaultCenter]removeObserver:self name:UIKeyboardWillHideNotification object:nil];
}```
** 键盘弹起修改动画**

-(void)openKeyboard:(NSNotification *)sender{
 - 弹起高度
  CGFloat keyboardHeight = [sender.userInfo[UIKeyboardFrameEndUserInfoKey]CGRectValue].size.height;
- 动画时长    
  CGFloat duration = [sender.userInfo[UIKeyboardAnimationDurationUserInfoKey]floatValue];
- 动画种类
  NSInteger option = [sender.userInfo[UIKeyboardAnimationCurveUserInfoKey]intValue];
- 修改约束
 self.bottomLayoutConstraint.constant = keyboardHeight;
  [UIView animateWithDuration:duration delay:0 options:option animations:^{
        [self.view layoutIfNeeded];
        //键盘弹起后滚动到最底部
        [self scrollToTableViewLastRow];
    } completion:nil];
}```
** 关闭键盘修改动画**

• (void)closeKeyboard:(NSNotification *)sender{
  CGFloat duration = [sender.userInfo[UIKeyboardAnimationDurationUserInfoKey]floatValue];
  NSInteger option = [sender.userInfo[UIKeyboardAnimationCurveUserInfoKey]intValue];
  self.bottomLayoutConstraint.constant = 0;

  [UIView animateWithDuration:duration delay:0 options:option animations:^{
  [self.view layoutIfNeeded];
  } completion:nil];
  }```

** 点击右下角返回按键，发消息，收键盘**

- (IBAction)clickReturnKey:(UITextField *)sender {
    NSString *newContent = self.textField.text;
    if (newContent.length == 0) {
        return;
    }
    //构建message对象
    Message *newMessage = [[Message alloc]init];
    newMessage.content = newContent;
    newMessage.fromMe = YES;
    
    //将新的message保存到模型中
    [self.allMessage addObject:newMessage];
    self.textField.text = @"";//清空文本框
    
    //局部刷新界面
    NSIndexPath *indexPath = [NSIndexPath indexPathForRow:self.allMessage.count-1 inSection:0];
    [self.tableView insertRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
    [self scrollToTableViewLastRow];
}```

**控制表视图滚动到最底部**

-(void)scrollToTableViewLastRow{
NSIndexPath *lastIndexPath = [NSIndexPath indexPathForRow:self.allMessage.count-1 inSection:0];
[self.tableView scrollToRowAtIndexPath:lastIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];
}```