render template widget correctly, fixes #1115, re #1102

Merge request studip/studip!666

lib/classes/sidebar/ResourceTreeWidget.class.php

@@ -116,12 +116,7 @@ class ResourceTreeWidget extends SidebarWidget
         $variables['max_open_depth'] = 0;
         $variables['layout_css_classes'] = $this->layout_css_classes;
 
-        $template = $GLOBALS['template_factory']->open(
-            $this->template
-        );
-        $template->set_attributes($variables);
-        $template->set_layout('sidebar/widget-layout');
-        return $template->render();
+        return parent::render($variables);
     }
 
     public function setCurrentResource(Resource $resource)

lib/classes/sidebar/SidebarWidget.php

@@ -11,12 +11,32 @@ class SidebarWidget extends Widget
 {
     protected $additional_attributes = [];
 
-
     public function __construct()
     {
         $this->layout = 'sidebar/widget-layout.php';
     }
 
+    /**
+     * Sets the ID of the HTML element that represents the widget.
+     *
+     * @param $id The element-ID to be used for the widget.
+     *
+     */
+    public function setId(string $id)
+    {
+        $this->id = $id;
+    }
+
+    /**
+     * Returns the ID of this widget, if it is set.
+     *
+     * @return string The ID of the widget or an empty string, if it is not set.
+     */
+    public function getId() : string
+    {
+        return $this->id ?? '';
+    }
+
     /**
      * Sets the title of the widget.
      *
@@ -77,7 +97,6 @@ class SidebarWidget extends Widget
         unset($this->additional_attributes[$key]);
     }
 
-
     /**
      * Renders the widget.
      * The widget will only be rendered if it contains at least one element.