Symfony: Access an unmapped form field from a CollectionType in Controller

Question

I have a form collection like this in Symfony 3.4:

// MainType.php

$builder->add('children', CollectionType::class, ['entry_type' => ChildType::class]);

// ChildType.php

$builder->add('myField', null, ['mapped' => false]);
// plus more fields, mapped to the underlying `Child` entity

// Controller

$form = $this->createForm(MainType::class, ['children' => $children]);
$form->handleRequest($request);
if ($form->isSubmitted() and $form->isValid()) {
    // How can I access the data of `myField` here?
}

When doing it the usual way with

$data = $form->getData();

...I'm getting an array of the Child entities, not the forms themselves.

So the question in other words is: In a form collection, how can I access the child forms , not the child entities ?

Answer 1

I couldn't find a solution anywhere, so I'm posting how I finally solved it:

/** @var Symfony\Component\Form\Form $formChild */
foreach ($form->get('children') as $formChild)
{
    $formChild->get('myField')->getData(); // That's it!
}

The basic principle is explained at https://symfony.com/doc/current/form/without_class.html