Ok, can’t find it anywhere so let see if somebody knows

In the administration I have some custom actions, for example I have a gridfield button that deletes all records.

How do I display a success of failure message on the screen to the admin user.

I use this code

class GridFieldDeleteAllButton implements GridField_HTMLProvider, GridField_ActionProvider {
	protected $targetFragment;

	public function __construct($targetFragment = "before") {
		$this->targetFragment = $targetFragment;
	}

	public function getHTMLFragments($gridField) {
		$button = new GridField_FormAction(
			$gridField,
			'deleteall',
			_t('TableListField.DELETEALL', 'Delete All'),
			'deleteall',
			null
		);
		$button->setAttribute('data-icon', 'cross-circle');
		$button->addExtraClass('deleteWithConfirm gridfield-better-buttons-delete');
		return array(
			$this->targetFragment => '<p class="grid-del-button">' . $button->Field() . '</p>',
		);
	}

	public function getActions($gridField) {
		return array('deleteall');
	}

	public function handleAction(GridField $gridField, $actionName, $arguments, $data) {
		if($actionName == 'deleteall') {
			return $this->handleDeleteAll($gridField);
		}
	}

	public function handleDeleteAll($gridField, $request = null) {
		//Add your own DELETE logic here !
		$items=$gridField->getList();
		foreach ($items as $item) {
			$item->hide = 1;
			$item->AddDate = date('Y-m-d H:i:s');
			//$item->write();
			Debug::show($item->ID);
		}
		Controller::curr()->redirectBack();
	}
}