fix header not updated on web

example/lib/chat_example.dart

@@ -1,5 +1,4 @@
 import 'dart:async';
-import 'dart:math';
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
@@ -97,7 +96,7 @@ List<Message> get getOlderMessages => [
     ];
 
 class MyApp extends StatefulWidget {
-  const MyApp({Key? key}) : super(key: key);
+  const MyApp({super.key});
 
   @override
   State<MyApp> createState() => _MyAppState();
@@ -268,7 +267,7 @@ class _ChatTimelineState extends State<ChatTimeline> {
 }
 
 class FakeMessageTextField extends StatelessWidget {
-  const FakeMessageTextField({Key? key}) : super(key: key);
+  const FakeMessageTextField({super.key});
 
   @override
   Widget build(BuildContext context) {
@@ -302,12 +301,12 @@ class FakeMessageTextField extends StatelessWidget {
             maxLines: 8,
             decoration: InputDecoration(
               prefixIcon: IconButton(
-                onPressed: () => null,
+                onPressed: () {},
                 icon: Icon(Icons.camera_alt_outlined,
                     color: Theme.of(context).primaryColor),
               ),
               suffixIcon: IconButton(
-                onPressed: () => null,
+                onPressed: () {},
                 icon: Icon(Icons.send, color: Theme.of(context).primaryColor),
               ),
             ),

example/lib/example.dart

@@ -13,7 +13,7 @@ List _elements = [
 ];
 
 class MyApp extends StatelessWidget {
-  const MyApp({Key? key}) : super(key: key);
+  const MyApp({super.key});
 
   @override
   Widget build(BuildContext context) {
@@ -48,7 +48,7 @@ class MyApp extends StatelessWidget {
           style: const TextStyle(fontSize: 20, fontWeight: FontWeight.bold),
         ),
       ),
-      itemBuilder: (c, element) {
+      itemBuilder: (c, element, prevElement) {
         return Card(
           elevation: 8.0,
           margin: const EdgeInsets.symmetric(horizontal: 10.0, vertical: 6.0),

example/lib/section_example.dart

@@ -13,7 +13,7 @@ List _elements = [
 ];
 
 class MyApp extends StatelessWidget {
-  const MyApp({Key? key}) : super(key: key);
+  const MyApp({super.key});
 
   @override
   Widget build(BuildContext context) {
@@ -48,7 +48,7 @@ class MyApp extends StatelessWidget {
           style: const TextStyle(fontSize: 20, fontWeight: FontWeight.bold),
         ),
       ),
-      itemBuilder: (c, element) {
+      itemBuilder: (c, element, prevElement) {
         return Card(
           elevation: 8.0,
           margin: const EdgeInsets.symmetric(horizontal: 10.0),

example/lib/silver_example.dart

@@ -13,7 +13,7 @@ List _elements = [
 ];
 
 class MyApp extends StatelessWidget {
-  const MyApp({Key? key}) : super(key: key);
+  const MyApp({super.key});
 
   @override
   Widget build(BuildContext context) {

example/lib/stream_example.dart

@@ -15,7 +15,7 @@ List<Element> _elements = [];
 int counter = 1;
 
 class MyApp extends StatelessWidget {
-  const MyApp({Key? key}) : super(key: key);
+  const MyApp({super.key});
 
   @override
   Widget build(BuildContext context) {
@@ -57,7 +57,7 @@ class MyApp extends StatelessWidget {
       order: GroupedListOrder.DESC,
       useStickyGroupSeparators: true,
       groupSeparatorBuilder: (int groupValue) => _createGroupHeader(groupValue),
-      itemBuilder: (ctx, element) => _createItem(element.name),
+      itemBuilder: (ctx, element, prevElement) => _createItem(element.name),
     );
   }
 

lib/grouped_list.dart

@@ -60,7 +60,8 @@ class GroupedListView<T, E> extends StatefulWidget {
 
   /// Called to build children for the list with
   /// 0 <= element < elements.length.
-  final Widget Function(BuildContext context, T element)? itemBuilder;
+  final Widget Function(BuildContext context, T element, T? prevElement)?
+      itemBuilder;
 
   /// Called to build the children for the list where the current element
   /// depends of the previous and next elements
@@ -290,7 +291,11 @@ class _GroupedListViewState<T, E> extends State<GroupedListView<T, E>> {
   void initState() {
     _controller = widget.controller ?? ScrollController();
     if (widget.useStickyGroupSeparators) {
-      _controller.addListener(_scrollListener);
+      _controller.addListener(() {
+        WidgetsBinding.instance.addPostFrameCallback((_) {
+          _scrollListener();
+        });
+      });
     }
     super.initState();
   }
@@ -425,6 +430,7 @@ class _GroupedListViewState<T, E> extends State<GroupedListView<T, E>> {
                     : widget.itemBuilder!(
                         context,
                         _sortedElements[index],
+                        index > 0 ? _sortedElements[index - 1] : null,
                       ),
       );
 

test/grouped_list_test.dart

@@ -26,7 +26,7 @@ void main() {
             order: GroupedListOrder.ASC,
             groupSeparatorBuilder: (dynamic element) =>
                 SizedBox(height: 50, child: Text('$element')),
-            itemBuilder: (_, dynamic element) => SizedBox(
+            itemBuilder: (_, dynamic element, dynamic prevElement) => SizedBox(
               height: 100,
               child: Text(element['name']),
             ),