added logic to save collections and display them

lib/pages/collections_page.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
 
+import '../model/collection.dart';
+import '../service/storage.dart';
 import '../widgets/create_bookmark_collection_dialog.dart';
 
 class CollectionsPage extends StatefulWidget {
@@ -11,23 +13,36 @@ class CollectionsPage extends StatefulWidget {
 }
 
 class _CollectionsPageState extends State<CollectionsPage> {
+  final collections = Storage.loadCollections();
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(),
       floatingActionButton: FloatingActionButton(
-        onPressed: () => showDialog(
-          context: context,
-          builder: (context) => CreateBookmarkCollectionDialog(),
-        ),
+        onPressed: onAddButtonPressed,
         child: Icon(Icons.add),
       ),
-      body: ListView(),
+      body: ListView.builder(
+        itemBuilder: itemBuilder,
+        itemCount: collections.length,
+      ),
     );
   }
 
   void onAddButtonPressed() => showDialog(
     context: context,
-    builder: (context) => CreateBookmarkCollectionDialog(),
+    builder: (context) =>
+        CreateBookmarkCollectionDialog(onSavePressed: onCollectionSaved),
   );
+
+  void onCollectionSaved(String name) {
+    collections.add(Collection(name: name));
+    setState(() {});
+    Storage.saveCollections(collections);
+  }
+
+  Widget itemBuilder(BuildContext context, int index) {
+    return ListTile(title: Text(collections.elementAt(index).name));
+  }
 }