Can load older posts on group page

lib/ui/screens/authorized_group_page_screen.dart

@@ -7,6 +7,7 @@ import 'package:comunic/ui/widgets/group_membership_widget.dart';
 import 'package:comunic/ui/widgets/like_widget.dart';
 import 'package:comunic/ui/widgets/post_create_form_widget.dart';
 import 'package:comunic/ui/widgets/posts_list_widget.dart';
+import 'package:comunic/ui/widgets/scroll_watcher.dart';
 import 'package:flutter/material.dart';
 
 /// Authorized group page screen
@@ -35,11 +36,23 @@ class AuthorizedGroupPageScreen extends StatefulWidget {
 class _AuthorizedGroupPageScreenState extends State<AuthorizedGroupPageScreen> {
   AdvancedGroupInfo get _group => widget.advancedGroupInfo;
 
+  // Allows load older posts when we reach the bottom of the page
+  final _postsKey = GlobalKey<PostsListWidgetState>();
+  ScrollWatcher _postsController;
+
+  @override
+  void initState() {
+    _postsController = ScrollWatcher(
+        onReachBottom: () => _postsKey.currentState.reachedPostsBottom());
+    super.initState();
+  }
+
   @override
   Widget build(BuildContext context) {
     return RefreshIndicator(
       onRefresh: () => widget.needRefresh(),
       child: ListView(
+        controller: _postsController,
         children: <Widget>[
           _buildGroupPageHeader(),
           _buildPostCreationArea(),
@@ -105,6 +118,7 @@ class _AuthorizedGroupPageScreenState extends State<AuthorizedGroupPageScreen> {
   /// Build the list of posts of the group
   Widget _buildGroupPagePostsList() {
     return PostsListWidget(
+      key: _postsKey,
       getPostsList: () => PostsHelper().getGroupPosts(_group.id),
       showPostsTarget: false,
       userNamesClickable: true,