NEW Initial SessionGridFieldStateManager implementation, for managing

GridField states in session.

src/Forms/GridField/GridFieldDetailForm_ItemRequest.php

@@ -454,6 +454,13 @@ class GridFieldDetailForm_ItemRequest extends RequestHandler
 
             $gridState = $this->gridField->getState(false);
             $actions->push(HiddenField::create($manager->getStateKey($this->gridField), null, $gridState));
+            if ($manager instanceof GridFieldStateStoreInterface) {
+                $stateRequestVar = $manager->getStateRequestVar();
+                $stateValue = $this->getRequest()->requestVar($stateRequestVar);
+                if ($stateValue) {
+                    $actions->push(HiddenField::create($stateRequestVar, '', $stateValue));
+                }
+            }
 
             $actions->push($this->getRightGroupField());
         } else { // adding new record

src/Forms/GridField/GridFieldStateStoreInterface.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace SilverStripe\Forms\GridField;
+
+interface GridFieldStateStoreInterface
+{
+    public function storeState(GridField $gridField, $value = null);
+
+    public function getStateRequestVar(): string;
+}

src/Forms/GridField/GridState.php

@@ -85,7 +85,7 @@ class GridState extends HiddenField
     public function getData()
     {
         if (!$this->data) {
-            $this->data = new GridState_Data();
+            $this->data = new GridState_Data([], $this);
         }
 
         return $this->data;
@@ -99,6 +99,11 @@ class GridState extends HiddenField
         return $this->grid->getList();
     }
 
+    public function getGridField(): GridField
+    {
+        return $this->grid;
+    }
+
     /**
      * Returns a json encoded string representation of this state.
      *

src/Forms/GridField/GridState_Data.php

@@ -10,29 +10,33 @@ namespace SilverStripe\Forms\GridField;
  */
 class GridState_Data
 {
+    use GridFieldStateAware;
 
     /**
      * @var array
      */
     protected $data;
 
+    protected GridState $state;
+
     protected $defaults = [];
 
-    public function __construct($data = [])
+    public function __construct($data = [], GridState $state = null)
     {
         $this->data = $data;
+        $this->state = $state;
     }
 
     public function __get($name)
     {
-        return $this->getData($name, new GridState_Data());
+        return $this->getData($name, new GridState_Data([], $this->state));
     }
 
     public function __call($name, $arguments)
     {
         // Assume first parameter is default value
         if (empty($arguments)) {
-            $default = new GridState_Data();
+            $default = new GridState_Data([], $this->state);
         } else {
             $default = $arguments[0];
         }
@@ -72,16 +76,25 @@ class GridState_Data
             $this->data[$name] = $default;
         } else {
             if (is_array($this->data[$name])) {
-                $this->data[$name] = new GridState_Data($this->data[$name]);
+                $this->data[$name] = new GridState_Data($this->data[$name], $this->state);
             }
         }
 
         return $this->data[$name];
     }
 
+    public function storeData()
+    {
+        $stateManager = $this->getStateManager();
+        if ($stateManager instanceof GridFieldStateStoreInterface) {
+            $stateManager->storeState($this->state->getGridField(), $this->state->Value());
+        }
+    }
+
     public function __set($name, $value)
     {
         $this->data[$name] = $value;
+        $this->storeData();
     }
 
     public function __isset($name)
@@ -92,6 +105,7 @@ class GridState_Data
     public function __unset($name)
     {
         unset($this->data[$name]);
+        $this->storeData();
     }
 
     public function __toString()

src/Forms/GridField/SessionGridFieldStateManager.php

@@ -0,0 +1,101 @@
+<?php
+
+namespace SilverStripe\Forms\GridField;
+
+use SilverStripe\Control\Controller;
+use SilverStripe\Control\HTTPRequest;
+
+/**
+ * Creates a unique key for managing GridField states in user Session, for both storage and retrieval.
+ * Only stores states and generates a session key if a state is requested to be stored
+ * (i.e. the state is changed from the default).
+ * If a session state key is present in the request, it will always be used instead of generating a new one.
+ */
+class SessionGridFieldStateManager implements GridFieldStateManagerInterface, GridFieldStateStoreInterface
+{
+    protected static $state_ids = [];
+
+    protected function getStateID(GridField $gridField, $create = false): ?string
+    {
+        $requestVar = $this->getStateRequestVar();
+        $sessionStateID = $gridField->getForm()->getRequestHandler()->getRequest()->requestVar($requestVar);
+        if (!$sessionStateID) {
+            $sessionStateID = Controller::curr()->getRequest()->requestVar($requestVar);
+        }
+        if ($sessionStateID) {
+            return $sessionStateID;
+        }
+        $stateKey = $this->getStateKey($gridField);
+        if (isset(self::$state_ids[$stateKey])) {
+            $sessionStateID = self::$state_ids[$stateKey];
+        } elseif ($create) {
+            $sessionStateID = substr(md5(time()), 0, 8);
+            // we don't want session state id to be strictly numeric, since this is used as a session key,
+            // and session keys in php has to be usable as variable names
+            if (is_numeric($sessionStateID)) {
+                $sessionStateID .= 'a';
+            }
+            self::$state_ids[$stateKey] = $sessionStateID;
+        }
+        return $sessionStateID;
+    }
+
+    public function storeState(GridField $gridField, $value = null)
+    {
+        $sessionStateID = $this->getStateID($gridField, true);
+        $sessionState = Controller::curr()->getRequest()->getSession()->get($sessionStateID);
+        if (!$sessionState) {
+            $sessionState = [];
+        }
+        $stateKey = $this->getStateKey($gridField);
+        $sessionState[$stateKey] = $value ?? $gridField->getState(false)->Value();
+        Controller::curr()->getRequest()->getSession()->set($sessionStateID, $sessionState);
+    }
+
+    public function getStateRequestVar(): string
+    {
+        return 'gridSessionState';
+    }
+    
+    /**
+     * @param GridField $gridField
+     * @return string
+     */
+    public function getStateKey(GridField $gridField): string
+    {
+        $record = $gridField->getForm()->getRecord();
+        return $gridField->getName() . '-' . ($record ? $record->ID : 0);
+    }
+
+    /**
+     * @param GridField $gridField
+     * @param string $url
+     * @return string
+     */
+    public function addStateToURL(GridField $gridField, string $url): string
+    {
+        $sessionStateID = $this->getStateID($gridField);
+        if ($sessionStateID) {
+            return Controller::join_links($url, '?' . $this->getStateRequestVar() . '=' . $sessionStateID);
+        }
+        return $url;
+    }
+
+    /**
+     * @param GridField $gridField
+     * @param HTTPRequest $request
+     * @return string|null
+     */
+    public function getStateFromRequest(GridField $gridField, HTTPRequest $request): ?string
+    {
+        $gridSessionStateID = $request->requestVar($this->getStateRequestVar());
+        if ($gridSessionStateID) {
+            $sessionState = $request->getSession()->get($gridSessionStateID);
+            $stateKey = $this->getStateKey($gridField);
+            if ($sessionState && isset($sessionState[$stateKey])) {
+                return $sessionState[$stateKey];
+            }
+        }
+        return null;
+    }
+}