Php 在提交前向Symfony表单添加其他字段

我用的是痛风，代码如下

$client = new Client();

$crawler = $client->request('GET', \Config::get('Eload2::url'));

$form = $crawler->selectButton('Submit')->form();

// add extra fields here

$client->submit($form);

$domdocument = new \DOMDocument;

$formfield = new InputFormField ($domdocument->createElement('__EVENTTARGET', 'ctl00$ContentPlaceHolder1$DDLTelco'));

$formfield2 = new InputFormField ($domdocument->createElement('__EVENTARGUMENT',''));

$form->set($formfield); 

$form->set($formfield2);

如何在表单提交之前向表单添加隐藏的输入字段

我尝试了以下代码

$client = new Client();

$crawler = $client->request('GET', \Config::get('Eload2::url'));

$form = $crawler->selectButton('Submit')->form();

// add extra fields here

$client->submit($form);

$domdocument = new \DOMDocument;

$formfield = new InputFormField ($domdocument->createElement('__EVENTTARGET', 'ctl00$ContentPlaceHolder1$DDLTelco'));

$formfield2 = new InputFormField ($domdocument->createElement('__EVENTARGUMENT',''));

$form->set($formfield); 

$form->set($formfield2);

但返回以下错误消息

InputFormField只能从输入或按钮标记创建（\uu\u EVENTTARGET给定）

---

您正在创建的是：

<__EVENTTARGET>ctl00$ContentPlaceHolder1$DDLTelco</__EVENTTARGET>
<__EVENTARGUMENT />

---

您正在创建的是：

<__EVENTTARGET>ctl00$ContentPlaceHolder1$DDLTelco</__EVENTTARGET>
<__EVENTARGUMENT />