图片上传不适用于swift alamofire和php

import Alamofire

let image = UIImage(named: "example.jpg")
let imageData = image!.jpegData(compressionQuality: 0.8)

AF.upload(multipartFormData: { multipartFormData in
    multipartFormData.append(imageData!, withName: "image", fileName: "example.jpg", mimeType: "image/jpeg")
}, to: "http://example.com/upload")
    .response { response in
        debugPrint(response)
    }

<?php
$targetDir = "uploads/";
$targetFile = $targetDir . basename($_FILES["file"]["name"]);
$uploadOk = 1;
$imageFileType = strtolower(pathinfo($targetFile,PATHINFO_EXTENSION));

// 检查文件是否为图片
if(isset($_POST["submit"])) {
    $check = getimagesize($_FILES["file"]["tmp_name"]);
    if($check !== false) {
        echo "文件是一个图片 - " . $check["mime"] . ".";
        $uploadOk = 1;
    } else {
        echo "文件不是一个图片.";
        $uploadOk = 0;
    }
}

// 检查文件是否已存在
if (file_exists($targetFile)) {
    echo "文件已存在.";
    $uploadOk = 0;
}

// 限制文件大小
if ($_FILES["file"]["size"] > 500000) {
    echo "文件过大.";
    $uploadOk = 0;
}

// 允许的文件格式
if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg"
&& $imageFileType != "gif" ) {
    echo "只允许上传 JPG, JPEG, PNG 和 GIF 格式的文件.";
    $uploadOk = 0;
}

// 检查上传状态
if ($uploadOk == 0) {
    echo "文件上传失败.";
} else {
    if (move_uploaded_file($_FILES["file"]["tmp_name"], $targetFile)) {
        echo "文件上传成功.";
    } else {
        echo "文件上传失败.";
    }
}
?>