adds new components to the gallery

cupertino_gallery/lib/widgets/alert_dialog_page.dart

@@ -6,9 +6,7 @@ class AlertDialogPage extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return CupertinoPageScaffold(
-      navigationBar: const CupertinoNavigationBar(
-        middle: Text('Alert Dialog'),
-      ),
+      navigationBar: const CupertinoNavigationBar(middle: Text('Alert Dialog')),
       child: Center(
         child: CupertinoButton(
           child: const Text('Show Alert Dialog'),
@@ -25,6 +23,13 @@ class AlertDialogPage extends StatelessWidget {
                       Navigator.pop(context);
                     },
                   ),
+                  CupertinoDialogAction(
+                    isDefaultAction: true,
+                    child: const Text('NO'),
+                    onPressed: () {
+                      Navigator.pop(context);
+                    },
+                  ),
                 ],
               ),
             );