ENH Restore gridfield state from get vars

src/Forms/GridField/GridField.php

@@ -4,10 +4,12 @@
 
 use InvalidArgumentException;
 use LogicException;
+use SilverStripe\Control\Controller;
 use SilverStripe\Control\HasRequestHandler;
 use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Control\HTTPResponse;
 use SilverStripe\Control\HTTPResponse_Exception;
+use SilverStripe\Control\NullHTTPRequest;
 use SilverStripe\Control\RequestHandler;
 use SilverStripe\Core\Convert;
 use SilverStripe\Core\Injector\Injector;
@@ -45,6 +47,8 @@
  */
 class GridField extends FormField
 {
+    use GridFieldStateAware;
+
     /**
      * @var array
      */
@@ -435,6 +439,8 @@ private function initState(): void
     {
         $this->state = new GridState($this);
 
+        $this->addStateFromRequest();
+
         $data = $this->state->getData();
 
         foreach ($this->getComponents() as $item) {
@@ -444,6 +450,32 @@ private function initState(): void
         }
     }
 
+    /**
+     * Adds state for this gridfield from the request variables.
+     *
+     * If there is state already set on this GridField, that takes precedent
+     * over state from the request.
+     */
+    private function addStateFromRequest(): void
+    {
+        $request = $this->getRequest();
+        if (($request instanceof NullHTTPRequest) && Controller::has_curr()) {
+            $request = Controller::curr()->getRequest();
+        }
+        if ($request->params()['Action']) {
+            return;
+        }
+        $stateStr = $this->getStateManager()->getStateFromRequest($this, $request);
+        if ($stateStr) {
+            $oldState = $this->getState(false);
+            // Create a dummy state so that we can merge the current state with the request state.
+            $newState = new GridState($this, $stateStr);
+            // Put the current state on top of the request state.
+            $newState->setValue($oldState->Value());
+            $this->state = $newState;
+        }
+    }
+
     /**
      * Returns the whole gridfield rendered with all the attached components.
      *