minor #8969 Updated the "custom data collector" article (javiereguiluz)

This PR was squashed before being merged into the 3.4 branch (closes #8969).

Discussion
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Updated the "custom data collector" article

  This fixes #8935.

Commits
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d40fc1f Updated the "custom data collector" article

Author: javiereguiluz

profiler/data_collector.rst

@@ -4,43 +4,22 @@
 How to Create a custom Data Collector
 =====================================
 
-The :doc:`Symfony Profiler </profiler>` delegates data collection
-to some special classes called data collectors. Symfony comes bundled with a few
-of them, but you can easily create your own.
+The :doc:`Symfony Profiler </profiler>` obtains its profiling and debug
+information using some special classes called data collectors. Symfony comes
+bundled with a few of them, but you can also create your own.
 
 Creating a custom Data Collector
 --------------------------------
 
-Creating a custom data collector is as simple as implementing the
-:class:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollectorInterface`::
+A data collector is a PHP class that implements the
+:class:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollectorInterface`.
+For convenience, your data collectors can also extend from the
+:class:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollector` class, which
+implements the interface and provides some utilities and the ``$this->data``
+property to store the collected information.
 
-    interface DataCollectorInterface
-    {
-        function collect(Request $request, Response $response, \Exception $exception = null);
-        function getName();
-    }
-
-The
-:method:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollectorInterface::getName`
-method returns the name of the data collector and must be unique in the
-application. This value is also used to access the information later on (see
-:doc:`/testing/profiling` for instance).
-
-The
-:method:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollectorInterface::collect`
-method is responsible for storing the collected data in local properties.
-
-.. caution::
-
-    The ``collect()`` method is only called once. It is not used to "gather"
-    data but is there to "pick up" the data that has been stored by your
-    service.
-
-Most of the time, it is convenient to extend
-:class:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollector` and
-populate the ``$this->data`` property (it takes care of serializing the
-``$this->data`` property). Imagine you create a new data collector that
-collects the method and accepted content types from the request::
+The following example shows a custom collector that stores information about the
+request::
 
     // src/AppBundle/DataCollector/RequestCollector.php
     namespace AppBundle\DataCollector;
@@ -59,36 +38,46 @@ collects the method and accepted content types from the request::
             );
         }
 
-        public function getMethod()
+        public function reset()
         {
-            return $this->data['method'];
-        }
-
-        public function getAcceptableContentTypes()
-        {
-            return $this->data['acceptable_content_types'];
+            $this->data = array();
         }
 
         public function getName()
         {
             return 'app.request_collector';
         }
+
+        // ...
     }
 
-The getters are added to give the template access to the collected information.
+:method:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollectorInterface::collect` method:
+    Stores the collected data in local properties (``$this->data`` if you extend
+    from :class:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollector`).
+    If the data to collect cannot be obtained through the request or response,
+    inject the needed services in the data collector.
 
-.. caution::
+    .. caution::
 
-    If the data that is not directly related to the request or response,
-    you need to make the data accessible to your DataCollector. This can
-    be achieved by injecting the service that holds the information you intend
-    to profile into your DataCollector.
+        The ``collect()`` method is only called once. It is not used to "gather"
+        data but is there to "pick up" the data that has been stored by your
+        service.
 
-.. caution::
+    .. caution::
 
-    As the profiler serializes data collector instances, you should not
-    store objects that cannot be serialized (like PDO objects) or you need
-    to provide your own ``serialize()`` method.
+        As the profiler serializes data collector instances, you should not
+        store objects that cannot be serialized (like PDO objects) or you need
+        to provide your own ``serialize()`` method.
+
+:method:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollectorInterface::reset` method:
+    It's called between requests to reset the state of the profiler. Use it to
+    remove all the information collected with the ``collect()`` method.
+
+:method:`Symfony\\Component\\HttpKernel\\DataCollector\\DataCollectorInterface::getName` method:
+    Returns the collector identifier, which must be unique in the application.
+    This value is used later to access the collector information (see
+    :doc:`/testing/profiling`) so it's recommended to return a string which is
+    short, lowercased and without white spaces.
 
 .. _data_collector_tag:
 
@@ -99,10 +88,8 @@ If you're using the :ref:`default services.yml configuration <service-container-
 with ``autoconfigure``, then Symfony will automatically see your new data collector!
 Your ``collect()`` method should be called next time your refresh.
 
-.. note::
-
-    If you're not using ``autoconfigure``, you can also :ref:`manually wire your service <services-explicitly-configure-wire-services>`
-    and :doc:`tag </service_container/tags>` it with ``data_collector``.
+If you're not using ``autoconfigure``, you can also :ref:`manually wire your service <services-explicitly-configure-wire-services>`
+and :doc:`tag </service_container/tags>` it with ``data_collector``.
 
 Adding Web Profiler Templates
 -----------------------------
@@ -111,6 +98,29 @@ The information collected by your data collector can be displayed both in the
 web debug toolbar and in the web profiler. To do so, you need to create a Twig
 template that includes some specific blocks.
 
+However, first you must add some getters in the data collector class to give the
+template access to the collected information::
+
+    // src/AppBundle/DataCollector/RequestCollector.php
+    namespace AppBundle\DataCollector;
+
+    use Symfony\Component\HttpKernel\DataCollector\DataCollector;
+
+    class RequestCollector extends DataCollector
+    {
+        // ...
+
+        public function getMethod()
+        {
+            return $this->data['method'];
+        }
+
+        public function getAcceptableContentTypes()
+        {
+            return $this->data['acceptable_content_types'];
+        }
+    }
+
 In the simplest case, you just want to display the information in the toolbar
 without providing a profiler panel. This requires to define the ``toolbar``
 block and set the value of two variables called ``icon`` and ``text``: