Bootstrap 4 Form Theme

Symfony provides several ways of integrating Bootstrap into your application. The most straightforward way is to add the required <link> and <script> elements in your templates (usually you only include them in the main layout template which other templates extend from):

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{# templates/base.html.twig #}

{# beware that the blocks in your template may be named different #}
{% block head_css %}
    <!-- Copy CSS from https://getbootstrap.com/docs/4.4/getting-started/introduction/#css -->
{% endblock %}
{% block head_js %}
    <!-- Copy JavaScript from https://getbootstrap.com/docs/4.4/getting-started/introduction/#js -->
{% endblock %}

If your application uses modern front-end practices, it’s better to use Webpack Encore and follow this tutorial to import Bootstrap’s sources into your SCSS and JavaScript files.

The next step is to configure the Symfony application to use Bootstrap 4 styles when rendering forms. If you want to apply them to all forms, define this configuration:

  • YAML
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    # config/packages/twig.yaml
twig:
    form_themes: ['bootstrap_4_layout.html.twig']
  • XML
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    <!-- config/packages/twig.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:twig="http://symfony.com/schema/dic/twig"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/twig
        https://symfony.com/schema/dic/twig/twig-1.0.xsd">

    <twig:config>
        <twig:form-theme>bootstrap_4_layout.html.twig</twig:form-theme>
        <!-- ... -->
    </twig:config>
</container>
  • PHP
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    // config/packages/twig.php
$container->loadFromExtension('twig', [
    'form_themes' => [
        'bootstrap_4_layout.html.twig',
    ],

    // ...
]);

If you prefer to apply the Bootstrap styles on a form to form basis, include the form_theme tag in the templates where those forms are used:

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{# ... #}
{# this tag only applies to the forms defined in this template #}
{% form_theme form 'bootstrap_4_layout.html.twig' %}

{% block body %}
    <h1>User Sign Up:</h1>
    {{ form(form) }}
{% endblock %}

Accessibility

The Bootstrap 4 framework has done a good job making it accessible for functional variations like impaired vision and cognitive ability. Symfony has taken this one step further to make sure the form theme complies with the WCAG 2.0 standard.

This does not mean that your entire website automatically complies with the full standard, but it does mean that you have come far in your work to create a design for all users.

Custom Forms

Bootstrap 4 has a feature called “custom forms”. You can enable that on your Symfony Form RadioType and CheckboxType by adding some classes to the label:

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{{ form_row(form.myRadio, {label_attr: {class: 'radio-custom'} }) }}
{{ form_row(form.myCheckbox, {label_attr: {class: 'checkbox-custom'} }) }}
{{ form_row(form.myCheckbox, {label_attr: {class: 'switch-custom'} }) }}

Labels and Errors

When you use the Bootstrap form themes and render the fields manually, calling form_label() for a checkbox/radio field doesn’t render anything. Due to Bootstrap internals, the label is already rendered by form_widget().

Form errors are rendered inside the <label> element to make sure there is a strong connection between the error and its <input>, as required by the WCAG 2.0 standard.