Merge pull request #6 from iptton/master

solves issue #5

example/lib/box.dart

@@ -23,6 +23,7 @@ class Box extends StatelessWidget {
           color: isInView ? Colors.lightGreen : Colors.amber,
           child: Text(
             '$id : $inViewTxt',
+            key: ValueKey("item-$id"),
             style: Theme.of(context).textTheme.display1,
           ),
         );

example/lib/main.dart

@@ -45,6 +45,7 @@ class _HomePageState extends State<HomePage> {
         body: TabBarView(
           children: <Widget>[
             MyList(
+              key: ValueKey("list1"),
               initialInViewIds: ['0'],
               inViewArea: Container(
                 height: 1.0,

example/pubspec.yaml

@@ -28,8 +28,9 @@ dependencies:
   cupertino_icons: ^0.1.2
 
 dev_dependencies:
-  flutter_test:
+  flutter_driver:
     sdk: flutter
+  test: any
 
 # For information on the generic Dart part of this file, see the
 # following page: https://dart.dev/tools/pub/pubspec

example/test_driver/app.dart

@@ -0,0 +1,10 @@
+
+import 'package:example/main.dart';
+import 'package:flutter/cupertino.dart';
+import 'package:flutter_driver/driver_extension.dart';
+
+void main(){
+  enableFlutterDriverExtension();
+
+  runApp(MyApp());
+}

example/test_driver/app_test.dart

@@ -0,0 +1,45 @@
+import 'package:flutter_driver/flutter_driver.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group("test scroll fast up and down", () {
+    FlutterDriver driver;
+
+    setUpAll(() async {
+      driver = await FlutterDriver.connect();
+    });
+
+    tearDownAll(() async {
+      driver?.close();
+    });
+
+    test("scroll fast", () async {
+      final listFinder = find.byValueKey("list1");
+      // scroll to item 1
+      await driver.scroll(listFinder, 0, -200, Duration(milliseconds: 100));
+
+      // hack: force the driver wait 500ms for the notification events be process
+      await driver.scroll(listFinder, 0, 0, Duration(milliseconds: 500));
+
+      var txt1 = await driver.getText(find.byValueKey("item-1"));
+      var txt2 = await driver.getText(find.byValueKey("item-2"));
+
+      // scroll up and down between item 1 & 2.
+      for (int i = 0; i < 11; ++i) {
+        await driver.scroll(listFinder, 0, -400, Duration(milliseconds: 100));
+        await driver.scroll(listFinder, 0, 400, Duration(milliseconds: 100));
+      }
+
+      // hack: force the driver wait 500ms for the notification events be process
+      await driver.scroll(listFinder, 0, 0, Duration(milliseconds: 500));
+
+      // expect item 1 notInView
+      var txt = await driver.getText(find.byValueKey("item-1"));
+      expect(txt, txt1);
+
+      // expect item 2 notInView
+      txt = await driver.getText(find.byValueKey("item-2"));
+      expect(txt, txt2);
+    });
+  });
+}

lib/inview_notifier_list.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 
+import 'package:flutter/foundation.dart' show describeIdentity;
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:stream_transform/stream_transform.dart';
@@ -111,7 +112,7 @@ class _InViewNotifierListState extends State<InViewNotifierList> {
     _streamController = StreamController<ScrollNotification>();
 
     _streamController.stream
-        .transform(throttle(widget.throttleDuration))
+        .audit(widget.throttleDuration)
         .listen(_inViewState.onScroll);
   }
 
@@ -181,6 +182,7 @@ class _InViewNotifierListState extends State<InViewNotifierList> {
           if (!_streamController.isClosed && isScrollDirection) {
             _streamController.add(notification);
           }
+          return false;
         },
       ),
     );
@@ -204,6 +206,11 @@ class _WidgetData {
   final String id;
 
   _WidgetData({@required this.context, @required this.id});
+
+  @override
+  String toString() {
+    return describeIdentity(this) + " id=$id";
+  }
 }
 
 ///Class that stores the context's of the widgets and String id's of the widgets that are
@@ -231,6 +238,7 @@ class InViewState extends ChangeNotifier {
 
   ///Add the widget's context and an unique string id that needs to be notified.
   void addContext({@required BuildContext context, @required String id}) {
+    _contexts.removeWhere((d) => d.id == id);
     _contexts.add(_WidgetData(context: context, id: id));
   }