Add necessary call to Form::isSubmitted and remove boilerplate

- Since Symfony 4.0 it's required to call `Form::isSubmitted()` before you call `Form::isValid()`
- Remove some unnecessary boilerplate code by using automatic parameter conversion and parameter injection of the `EntityManager`

Author: keichinger

form/form_collections.rst

@@ -687,15 +687,8 @@ the relationship between the removed ``Tag`` and ``Task`` object.
         use Doctrine\Common\Collections\ArrayCollection;
 
         // ...
-        public function edit($id, Request $request)
+        public function edit(Task $task, Request $request, EntityManagerInterface $entityManager)
         {
-            $entityManager = $this->getDoctrine()->getManager();
-            $task = $entityManager->getRepository(Task::class)->find($id);
-
-            if (!$task) {
-                throw $this->createNotFoundException('No task found for id '.$id);
-            }
-
             $originalTags = new ArrayCollection();
 
             // Create an ArrayCollection of the current Tag objects in the database
@@ -707,7 +700,7 @@ the relationship between the removed ``Tag`` and ``Task`` object.
 
             $editForm->handleRequest($request);
 
-            if ($editForm->isValid()) {
+            if ($editForm->isSubmitted() && $editForm->isValid()) {
 
                 // remove the relationship between the tag and the Task
                 foreach ($originalTags as $tag) {