thinkphp 怎么接收 ios端 POST过来的图片

$upload = new \Think\Upload();// 实例化上传类    
         $upload->maxSize   =     3145728 ;// 设置附件上传大小
         $upload->exts      =     array('jpg', 'gif', 'png', 'jpeg');// 
         $upload->savePath  =      '/Public/Uploads/images/';
         $info   =   $upload->upload();
         if(!$info) {// 上传错误提示错误信息
             $this->error($upload->getError());
         }
         这种方法接收不到呢？ 是哪里问题呢！求大牛告知

---

<?php
if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/pjpeg"))
&& ($_FILES["file"]["size"] < 20000))
  {
  if ($_FILES["file"]["error"] > 0)
    {
    echo "Return Code: " . $_FILES["file"]["error"] . "<br />";
    }
  else
    {
    echo "Upload: " . $_FILES["file"]["name"] . "<br />";
    echo "Type: " . $_FILES["file"]["type"] . "<br />";
    echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb<br />";
    echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br />";

    if (file_exists("upload/" . $_FILES["file"]["name"]))
      {
      echo $_FILES["file"]["name"] . " already exists. ";
      }
    else
      {
      move_uploaded_file($_FILES["file"]["tmp_name"],
      "upload/" . $_FILES["file"]["name"]);
      echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
      }
    }
  }
else
  {
  echo "Invalid file";
  }
?>