How to render a checkbox that is checked by default with the symfony2 Form Builder?

You can also just set the attr attribute in the form builder buildForm method:

$builder->add('isPublic', CheckboxType::class, array(
    'attr' => array('checked'   => 'checked'),
));

In Symfony >= 2.3 "property_path" became "mapped".

So:

$builder->add('checkboxName', 'checkbox', array('mapped' => false,
    'label' => 'customLabel',
    'data' => true, // Default checked
));

Setting the 'data' option works for me. I'm creating a non entity based form:

$builder->add('isRated','checkbox', array(
    'data' => true
));

In TWIG

If you wish to do this in the template directly:

{{ form_widget(form.fieldName, { 'attr': {'checked': 'checked'} }) }}

Use the FormBuilder::setData() method :

$builder->add('fieldName', 'checkbox', array('property_path' => false));
$builder->get('fieldName')->setData( true );

"property_path" to false cause this is a non-entity field (Otherwise you should set the default value to true using your entity setter).

Checkbox will be checked by default.

To complete a previous answer, with a multiple field you can do that to check all choices :

   'choice_attr' => function ($val, $key, $index) {
       return ['checked' => true];
   }

https://symfony.com/doc/3.3/reference/forms/types/choice.html#choice-attr

You should make changes to temporary object where entity is stored before displaying it on form. Something like next:

<?php

namespace KPI\AnnouncementsBundle\Form;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

class AnnouncementType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {  
        // ...        

        if ($options['data']->getDisplayed() === null) {
            $options['data']->setDisplayed(true);
        }

        // ...

        $builder
            ->add('displayed', 'checkbox', array(
                'required' => false
            ));
    }
}

As per documentation: http://symfony.com/doc/current/reference/forms/types/checkbox.html#value

To make a checkbox or radio button checked by default, use the data option.

UserBundle\Entity\User

let's assume that you have an entity called ( User ) and it has a member named isActive, You can set the checkbox to be checked by default by setting up isActive to true:

$user = new User();

// This will set the checkbox to be checked by default
$user->setIsActive(true);

// Create the user data entry form
$form = $this->createForm(new UserType(), $user);

I had the same problem as you and here is the only solution I found:

$builder->addEventListener(FormEvents::PRE_SET_DATA, function (FormEvent $event) {
    $entity= $event->getData();
    $form = $event->getForm();
    $form->add('active', CheckboxType::class, [
        'data' => is_null($entity) ? true : $entity->isActive(),
    ]);
});

This works as well, but aware of persistent "checked" state

$builder->add('isPublic', 'checkbox', array(
    'empty_data' => 'on',
));

This is how you can define the default values for multiple and expanded checkbox fields. Tested in Symfony4, but it has to work with Symfony 2.8 and above.

if you want to active the 1st and the 2nd checkboxes by default

class MyFormType1 extends AbstractType
{
    CONST FIELD_CHOICES = [
        'Option 1' => 'option_1',
        'Option 2' => 'option_2',
        'Option 3' => 'option_3',
        'Option 4' => 'option_4',
        'Option 5' => 'option_5',
    ];

    public function buildForm(FormBuilderInterface $builder, array $options)
    {

        $this->addSettingsField('my_checkbox_field', ChoiceType::class, [
            'label'    => 'My multiple checkbox field',
            'choices'  => self::FIELD_CHOICES,
            'expanded' => true,
            'multiple' => true,
            'data'     => empty($builder->getData()) ? ['option_1', 'option_2'] : $builder->getData(),
        ]);

    }
}

if you want to active every checkbox by default

class MyFormType2 extends AbstractType
{
    CONST FIELD_CHOICES = [
        'Option 1' => 'option_1',
        'Option 2' => 'option_2',
        'Option 3' => 'option_3',
        'Option 4' => 'option_4',
        'Option 5' => 'option_5',
    ];

    public function buildForm(FormBuilderInterface $builder, array $options)
    {

        $this->addSettingsField('my_checkbox_field', ChoiceType::class, [
            'label'    => 'My multiple checkbox field',
            'choices'  => self::FIELD_CHOICES,
            'expanded' => true,
            'multiple' => true,
            'data'     => empty($builder->getData()) ? array_values(self::FIELD_CHOICES) : $builder->getData(),
        ]);

    }
}

The only watertight solution for me in Symfony 4, 2022 is:

OPTION 1:

First, set it default to "true" on the entity parameter itself:

class MyEntity {
    /**
     * @ORM\Column(name="my_param", type="boolean", nullable=true)
     */
    private $myParameter = true;

    ...
}

Secondly, in the form, first see if you can get it from the entity itself. If Not, set the default

public function buildForm(FormBuilderInterface $builder, array $options)
{
    /** @var MyEntity $entity */
    $entity = $builder->getData();

    $builder->add('myParameter', CheckboxType::class, [
        'required' => false,
        'data' => $entity ? $entity->getMyParameter() : true,
    ]);
}

This way the real value (coming from the database) has precedence over the default value.
Also good to know is: Submitted data has precedence over the 'data' => true but initially loaded data before submit gets overridden by 'data' => true

OPTION 2:

An alternative way of setting it default true on the MyEntity Class you can choose to set it as default only just before creating the form. But then you always need the object to create the form with. So you then may not create a form without a given object

if (empty($entity)) {
    // Warning: Only if it's a new object, set the default
    $entity = new MyEntity();
    $entity->setMyParameter(true);
}

// For this option you must always give the form an entity
$form = $this->createForm(MyType::class, $entity);
$form->handleRequest($request);

So for this option you don't need to do anything special in the FormType

$builder->add('myParameter', CheckboxType::class, [
    'required' => false,
]);