[DOCS] Add tutorial for FormDataProvider (#2746)

Author: peterkraume

Documentation/Tutorials/ExtendNews/FormDataProvider/Index.rst

@@ -0,0 +1,76 @@
+.. _formDataProvider:
+
+================
+FormDataProvider
+================
+
+`FormDataProvider <https://docs.typo3.org/permalink/t3coreapi:formengine-datacompiling>`_
+can be used to offer form-handling beyond the options provided by `displayCond` and `eval` in the TCA.
+Among other things, a FormDataProvider allows dynamic TCA changes while records are loaded in the TYPO3 backend.
+
+Example
+-------
+
+This example explains how to make at least one image mandatory if the record is flagged as top news.
+
+1) Update TCA
+~~~~~~~~~~~~~
+
+Create the file `Configuration/TCA/Overrides/tx_news_domain_model_news.php` in your custom extension.
+See `here <ext-based-on-news>`_ how to create that extension.
+
+.. code-block:: php
+
+    <?php
+
+    defined('TYPO3') or die();
+
+    $GLOBALS['TCA']['tx_news_domain_model_news']['columns']['istopnews']['onChange'] = 'reload';
+
+With `'onChange' => 'reload'` you trigger a reload of the backend interface when the "Top news" toggle is clicked.
+
+2) Register FormDataProvider class
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Update file `ext_localconf.php` in your extension:
+
+.. code-block:: php
+
+    <?php
+
+    defined('TYPO3') or die();
+
+    use Vendor\CustomExtension\Backend\Form\FormDataProvider\ImageMinItems;
+    use TYPO3\CMS\Backend\Form\FormDataProvider\DatabaseRowInitializeNew;
+
+    $GLOBALS['TYPO3_CONF_VARS']['SYS']['formEngine']['formDataGroup']['tcaDatabaseRecord'][ImageMinItems::class] = [
+        'depends' => [
+            DatabaseRowInitializeNew::class,
+        ],
+    ];
+
+3) Add your FormDataProvider class
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: php
+
+    <?php
+
+    declare(strict_types=1);
+
+    namespace Vendor\CustomExtension\Backend\Form\FormDataProvider;
+
+    use TYPO3\CMS\Backend\Form\FormDataProviderInterface;
+
+    final class ImageMinItems implements FormDataProviderInterface
+    {
+        public function addData(array $result): array
+        {
+            if ($result['tableName'] == 'tx_news_domain_model_news' && $result['databaseRow']['istopnews'] == 1) {
+                $result['processedTca']['columns']['fal_media']['config']['minitems'] = 1;
+            }
+            return $result;
+        }
+    }
+
+This class modifies the TCA when the current record is `tx_news_domain_model_news` and `istopnews` is set.

Documentation/Tutorials/ExtendNews/Index.rst

@@ -45,6 +45,10 @@ Extend News
 
       Add additional custom news types
 
+   .. card:: :ref:`FormDataProvider <formDataProvider>`
+
+      Modify the TCA with the help of a FormDataProvider
+
 .. toctree::
    :maxdepth: 5
    :titlesonly:
@@ -58,3 +62,4 @@ Extend News
    DataProcessing/Index
    ProxyClassGenerator/Index
    AddCustomType/Index
+   FormDataProvider/Index