update: unit test

test/chat_scroll_observer_test.dart

@@ -0,0 +1,114 @@
+/*
+ * @Author: LinXunFeng [email protected]
+ * @Repo: https://github.com/fluttercandies/flutter_scrollview_observer
+ * @Date: 2023-11-25 19:04:30
+ */
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:scrollview_observer/scrollview_observer.dart';
+
+void main() {
+  // Regression test for https://github.com/fluttercandies/flutter_scrollview_observer/issues/64.
+  testWidgets('Keeping position', (tester) async {
+    final scrollController = ScrollController();
+    final observerController =
+        ListObserverController(controller: scrollController);
+    final chatScrollObserver = ChatScrollObserver(observerController)
+      ..fixedPositionOffset = -1;
+
+    int receiveScrollNotificationCount = 0;
+
+    Widget widget = ChatListView(
+      scrollController: scrollController,
+      observerController: observerController,
+      chatScrollObserver: chatScrollObserver,
+      onReceiveScrollNotification: () {
+        receiveScrollNotificationCount += 1;
+      },
+    );
+    await tester.pumpWidget(widget);
+    await tester.tap(find.byType(FloatingActionButton));
+    await tester.pumpAndSettle();
+
+    final result = await observerController.dispatchOnceObserve(
+      isForce: true,
+      isDependObserveCallback: false,
+    );
+    expect(result.observeResult?.firstChild?.index, 4);
+    expect(receiveScrollNotificationCount, 0);
+
+    scrollController.dispose();
+  });
+}
+
+class ChatListView extends StatefulWidget {
+  const ChatListView({
+    Key? key,
+    required this.scrollController,
+    required this.observerController,
+    required this.chatScrollObserver,
+    required this.onReceiveScrollNotification,
+  }) : super(key: key);
+
+  final ScrollController scrollController;
+  final ListObserverController observerController;
+  final ChatScrollObserver chatScrollObserver;
+  final Function()? onReceiveScrollNotification;
+
+  @override
+  State<ChatListView> createState() => _ChatListViewState();
+}
+
+class _ChatListViewState extends State<ChatListView> {
+  List<String> dataList =
+      List.generate(100, (index) => index.toString()).toList();
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Scaffold(
+        appBar: AppBar(),
+        body: _buildListView(),
+        floatingActionButton: FloatingActionButton(
+          onPressed: () {
+            widget.chatScrollObserver.standby(changeCount: 4);
+            setState(() {
+              dataList.insert(0, '-1');
+              dataList.insert(0, '-2');
+              dataList.insert(0, '-3');
+              dataList.insert(0, '-4');
+            });
+          },
+          child: const Icon(Icons.add),
+        ),
+      ),
+    );
+  }
+
+  Widget _buildListView() {
+    Widget resultWidget = ListViewObserver(
+      controller: widget.observerController,
+      child: ListView.builder(
+        itemCount: dataList.length,
+        physics: ChatObserverBouncingScrollPhysics(
+          observer: widget.chatScrollObserver,
+        ),
+        controller: widget.scrollController,
+        itemBuilder: (context, index) {
+          return SizedBox(
+            height: 100,
+            child: Center(child: Text(dataList[index])),
+          );
+        },
+      ),
+    );
+    resultWidget = NotificationListener<ScrollNotification>(
+      child: resultWidget,
+      onNotification: (notification) {
+        widget.onReceiveScrollNotification?.call();
+        return false;
+      },
+    );
+    return resultWidget;
+  }
+}