[core] add default pagination value + implement pagination in example

packages/stream_chat_flutter_core/example/lib/main.dart

@@ -67,6 +67,8 @@ class StreamExample extends StatelessWidget {
 /// [ChannelListCore] is a `builder` with callbacks for constructing UIs based
 /// on different scenarios.
 class HomeScreen extends StatelessWidget {
+  final channelListController = ChannelListController();
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -75,6 +77,15 @@ class HomeScreen extends StatelessWidget {
       ),
       body: ChannelsBloc(
         child: ChannelListCore(
+          channelListController: channelListController,
+          filter: {
+            'type': 'messaging',
+            'members': {
+              r'$in': [
+                StreamChatCore.of(context).user.id,
+              ]
+            }
+          },
           emptyBuilder: (BuildContext context) {
             return Center(
               child: Text('Looks like you are not in any channels'),
@@ -99,7 +110,11 @@ class HomeScreen extends StatelessWidget {
             BuildContext context,
             List<Channel> channels,
           ) =>
-              ListView.builder(
+              LazyLoadScrollView(
+            onEndOfPage: () async {
+              channelListController.paginateData();
+            },
+            child: ListView.builder(
               itemCount: channels.length,
               itemBuilder: (BuildContext context, int index) {
                 final _item = channels[index];
@@ -127,6 +142,7 @@ class HomeScreen extends StatelessWidget {
             ),
           ),
         ),
+      ),
     );
   }
 }

packages/stream_chat_flutter_core/lib/src/channel_list_core.dart

@@ -64,7 +64,10 @@ class ChannelListCore extends StatefulWidget {
     this.filter,
     this.options,
     this.sort,
-    this.pagination,
+    this.pagination = const PaginationParams(
+      offset: 0,
+      limit: 25,
+    ),
     this.channelListController,
   })  : assert(errorBuilder != null),
         assert(emptyBuilder != null),