Book/Form : Adding a new section about defining forms as service

book/forms.rst

@@ -833,6 +833,78 @@ form "type"). It can be used to quickly build a form object in the controller::
         // ...
     }
 
+.. tip::
+
+    Defining your form as a service is a good practice and make it easily usable in
+    your application. First, you must tag your form as a form type in the service container:
+
+        .. configuration-block::
+
+            .. code-block:: yaml
+
+                # src/Acme/TaskBundle/Resources/config/services.yml
+                services:
+                    acme_demo.form.type.task:
+                        class: Acme\TaskBundle\Form\Type\TaskType
+                        tags:
+                            - { name: form.type, alias: task }
+
+            .. code-block:: xml
+
+                <!-- src/Acme/TaskBundle/Resources/config/services.xml -->
+                <service id="acme_demo.form.type.task" class="Acme\TaskBundle\Form\Type\TaskType">
+                    <tag name="form.type" alias="task" />
+                </service>
+
+            .. code-block:: php
+
+                // src/Acme/TaskBundle/Resources/config/services.php
+                use Symfony\Component\DependencyInjection\Definition;
+
+                $container
+                    ->setDefinition('acme_demo.form.type.task', new Definition(
+                        'Acme\TaskBundle\Form\Type\TaskType'
+                    )
+                    ->addTag('form.type', array(
+                        'alias' => 'task',
+                    ))
+                ;
+
+    That's it! Now you can use your form directly in a controller::
+
+        // src/Acme/TaskBundle/Controller/DefaultController.php
+
+        public function newAction()
+        {
+            $task = ...;
+            $form = $this->createForm('task', $task);
+
+            // ...
+        }
+
+    or even use it as a normal type in another form::
+
+        // src/Acme/TaskBundle/Form/Type/ListType.php
+        namespace Acme\TaskBundle\Form\Type;
+
+        use Symfony\Component\Form\AbstractType;
+        use Symfony\Component\Form\FormBuilderInterface;
+
+        class ListType extends AbstractType
+        {
+            public function buildForm(FormBuilderInterface $builder, array $options)
+            {
+                // ...
+
+                $builder->add('task', 'task');
+                // Note that the property ``task`` (first argument) is defined as a ``task`` form type (second).
+            }
+
+            // ...
+        }
+
+    Read :ref:`form-cookbook-form-field-service` for more information.
+
 Placing the form logic into its own class means that the form can be easily
 reused elsewhere in your project. This is the best way to create forms, but
 the choice is ultimately up to you.