Detection Form Validation

I have a dynamic form.

For exemple, if something, my form contains FormType1 else my form contains FormType2 or FormType3 ....

I would detect if my form is modify.
If my form is completed, I apply is valid() method and if there is an error I return in the form or if there is no error, I apply a redirection.
I know how to do that.

But, if my fom was submitted without modifications (with no new value) I want to apply an other redirection without validation because my validation will return false with required fields.

I can't test if all values are null because in form there may be combobox or boolean, or initial value, ...

I have a solution with javascript and two submit buttons.
If the value of button submit is 'just_redirection' I don't apply the validation else I apply validation.

Is there a way in Symfony2 (or full PHP) to know if the submitted form is the same that the initial form?

Let's assume your form is bound with an entity MyEntity, in your controller you need to copy your original object, let the form handle the request, then compare your objects:

public function aRouteAction(Request $request, MyEntity $myEntity)
{
    $entityFromForm = clone $myEntity;
    // you need to clone your object, because since PHP5 a variable contains a reference to the object, so $entityFromForm = $myEntity wouldn't work

    $form = $this->createForm(new MyFormType(), $entityFromForm);
    $form->handleRequest($request);

    if($entityFromForm == $myEntity) {
        // redirect when no changes
    }

    if($form->isValid()) {
        // redirect when there are changes and form submission is valid
    }
    else {
        // return errors
    }
}

For object cloning please refer to the php manual.