错误：我要上传和编辑图片时

Question

这样的问题，当我要上传照片时，总是会出现这样的代码

A PHP Error was encountered
Severity: Warning
Message: Illegal string offset 'file_name'
Filename: controllers/product.php
Line Number: 113

Backtrace:

File: C:\xampp\htdocs\test\application\modules\admin\controllers\product.php
Line: 113
Function: _error_handler

我该如何解决？谢谢

我的控制器

if(!empty($_FILES['photo']['name']))
  {
     $upload = $this->_do_upload();
     $data['photo'] = $upload['file_name'];
}