Order of Symfony form CollectionType field

You need to use finishView method of your form type.

Here is the example of code:

public function finishView(FormView $view, FormInterface $form, array $options){    usort($view['photos']->children, function (FormView $a, FormView $b) {        /** @var Photo $objectA */        $objectA = $a->vars['data'];        /** @var Photo $objectB */        $objectB = $b->vars['data'];        $posA = $objectA->getSortOrder();        $posB = $objectB->getSortOrder();        if ($posA == $posB) {            return 0;        }        return ($posA < $posB) ? -1 : 1;    });}

It is possible to combine arrow function https://www.php.net/manual/en/functions.arrow.php with spaceship https://www.php.net/manual/en/migration70.new-features.php with PHP 7.

With the previous example :

public function finishView(FormView $view, FormInterface $form, array $options){    usort($view['photos']->children, fn (FormView $a, FormView $b) => $a->vars['data']->getSortOrder() <=> $b->vars['data']->getSortOrder());}

A more advanced example, ordered any collection from everywhere by using any ordered field :

public function finishView(FormView $view, FormInterface $form, array $options){    $view['blocks']->children = array_merge($view['blockTexts']->children, $view['blockImages']->children);    usort($view['blocks']->children, fn (FormView $a, FormView $b) => $a->vars['data']->orderNumber <=> $b->vars['data']->orderNumber);}