Checkboxtype doesn't change value according to the related object

I have a class Measure with a boolean property named "isShared"

/**
 * @ORM\Entity(repositoryClass="App\Repository\MeasureRepository")
 * @UniqueEntity("name", message = "This value is already used")
 */
class Measure
{
    /**
     * @ORM\Id
     * @ORM\GeneratedValue
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(name="is_shared", type="boolean")
     */
    private $isShared;
}

And a form in which the value of the value of the isShared property should be changed through a checkbox.

class MeasureType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('isShared', CheckboxType::class, array(
                'required' => false,
                'label' => 'Shared',
                'attr' => array(
                    'data-on-color' => 'primary',
                    'data-off-color' => 'default'
                )
            ));
}

The problem is that the rendered html is always

<input type="checkbox" id="measure_isShared" name="measure[isShared]" data-on-color="primary" data-off-color="default" value="1" /> Shared</label>

not taking into account the value of the property in the object. When I pass to the form a Measure object with the property isShared set to false, the value of the input is always 1.

What I'm doing wrong? Thank you!