Expected argument of type "string", "Vendor\NameBundle\Form\EntitynameType" given Symfony 3.0

Forms have changed quite a bit in 3.0. You might be better off sticking with 2.8 for now.

You did not show it but I suspect, based on the error message, that your controller code looks like:

$form = $this->createForm(new ReservernType(), $item);

That is the 2.x way of doing things. For 3.x use:

$form = $this->createForm(ReservernType::class, $item);

http://symfony.com/doc/current/book/forms.html#creating-form-classes

try with:

$builder        ->add('naam', TextType::class);        // If you use PHP 5.3 or 5.4 you must use        // ->add('naam','Symfony\Component\Form\Extension\Core\Type\TextType')

instead of this

$builder    ->add('naam');

And add the use statement:

use Symfony\Component\Form\Extension\Core\Type\TextType;

Motivation: from the upgrade guide:

Type names were deprecated and will be removed in Symfony 3.0. Instead of referencing types by name, you should reference them by their fully-qualified class name (FQCN) instead. With PHP 5.5 or later, you can use the "class" constant for that:

Hope this help

Try like this:

/.../use Symfony\Component\Form\Extension\Core\Type\TextType; /.../class ReserverenType extends AbstractType{    public function buildForm(FormBuilderInterface $builder, array $options)    {           $builder->add('naam', TextType::class);    }}