更新约束动画

    _isOrderOpen = !_isOrderOpen;
    [UIView animateWithDuration:0.5 animations:^{
        if (_isOrderOpen) {
            _orderControlConstant.constant = 50;
        } else {
            _orderControlConstant.constant = 0;
        }
        [self.view layoutIfNeeded];
    }];
原文地址:https://www.cnblogs.com/10-19-92/p/5504372.html