弹出键盘时UITableview内容跟着上移，不至于被键盘挡住，导致UITableView内容显示不完

//首先注册通知，监听键盘：

- (void)viewDidLoad {
    [super viewDidLoad];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillAppear:) name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillDisAppear:) name:UIKeyboardWillHideNotification object:nil];
}

 //在键盘弹出和收起的方法中做以下操作

- (void)keyboardWillAppear:(NSNotification *)noti {
    NSDictionary *userInfo = noti.userInfo;
    //获取键盘的frame
    CGRect keyboardFrame = [[userInfo objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue];
    //获取键盘弹出的动画时间
    NSTimeInterval animationDuration = [[userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey ] doubleValue];
    //让输入框跟随变化
    [UIView animateWithDuration:animationDuration animations:^{
       [_ctv mas_updateConstraints:^(MASConstraintMaker *make) {
           make.bottom.equalTo(@(-keyboardFrame.size.height));
       }];
    }];
    //设置tableview的contentInset属性，改变tableview的显示范围
    _tableView.contentInset = UIEdgeInsetsMake(0, 0, keyboardFrame.size.height, 0);
    _tableView.scrollEnabled = YES;
}

- (void)keyboardWillDisAppear:(NSNotification *)noti {
    NSDictionary *userInfo = noti.userInfo;
    NSTimeInterval animationDuration = [[userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey ] doubleValue];
    [UIView animateWithDuration:animationDuration animations:^{
        [_ctv mas_updateConstraints:^(MASConstraintMaker *make) {
            make.bottom.equalTo(@0);
            make.height.equalTo(@52);
        }];
    }];
    UIEdgeInsets contentInsets = UIEdgeInsetsZero;
    _tableView.contentInset = contentInsets;
}