追加数组FORMDATA和发送通过AJAX

我用ajax提交与阵列，文本字段和文件的多部分的形式。

I'm using ajax to submit a multipart form with array, text fields and files.

我每次追加VAR的主要数据为这样

I append each VAR to the main data as so

var attachments = document.getElementById('files'); 
var data= new FormData();

for (i=0; i< attachments.files.length; i++){
    data.append('file', attachments.files[i]);
    console.log(attachments.files[i]);

    data.append ('headline', headline);
    data.append ('article', article);
    data.append ('arr', arr);
    data.append ('tag', tag);

比我使用AJAX功能，将其发送到一个PHP文件来存储SQL数据库里面。

than I use the ajax function to send it to a PHP file to store inside sql DB.

$.ajax({    
    type: "post",
    url: 'php/submittionform.php',
    cache: false,
    processData: false,
    contentType: false,
    data: data,
    success: function(request) {$('#box').html(request); }
})

但在PHP端时，改编变量，它是一个数组显示为一个字符串。

But on the PHP side, the arr variable, which is an array appears as a string.

当我不为表数据与阿贾克斯发送，但使用简单的 $。POST 选项我得到它作为在PHP端阵列，但随后我不能发送的文件。

When I don't send it with ajax as Form data but use the simple $.POST option I do get it as an array on the PHP side, but then I can't send the files as well.

任何解决方案？