Revert "[new feature]introduce `ScrollMetricsNotification` (#85221)" (#85466)

packages/flutter/lib/src/widgets/scroll_position.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/physics.dart';
@@ -12,7 +10,6 @@ import 'package:flutter/scheduler.dart';
 
 import 'basic.dart';
 import 'framework.dart';
-import 'notification_listener.dart';
 import 'page_storage.dart';
 import 'scroll_activity.dart';
 import 'scroll_context.dart';
@@ -511,17 +508,6 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
   ScrollMetrics? _lastMetrics;
   Axis? _lastAxis;
 
-  bool _isMetricsChanged() {
-    assert(haveDimensions);
-    final ScrollMetrics currentMetrics = copyWith();
-
-    return _lastMetrics == null ||
-      !(currentMetrics.extentBefore == _lastMetrics!.extentBefore
-      && currentMetrics.extentInside == _lastMetrics!.extentInside
-      && currentMetrics.extentAfter == _lastMetrics!.extentAfter
-      && currentMetrics.axisDirection == _lastMetrics!.axisDirection);
-  }
-
   @override
   bool applyContentDimensions(double minScrollExtent, double maxScrollExtent) {
     assert(minScrollExtent != null);
@@ -551,14 +537,7 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
       _pendingDimensions = false;
     }
     assert(!_didChangeViewportDimensionOrReceiveCorrection, 'Use correctForNewDimensions() (and return true) to change the scroll offset during applyContentDimensions().');
-
-    if (_isMetricsChanged()) {
-      // It isn't safe to trigger the ScrollMetricsNotification if we are in
-      // the middle of rendering the frame, the developer is likely to schedule
-      // a new frame(build scheduled during frame is illegal).
-      scheduleMicrotask(didUpdateScrollMetrics);
     _lastMetrics = copyWith();
-    }
     return true;
   }
 
@@ -919,13 +898,6 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
     UserScrollNotification(metrics: copyWith(), context: context.notificationContext!, direction: direction).dispatch(context.notificationContext);
   }
 
-  /// Dispatches a notification that the [ScrollMetrics] has changed.
-  void didUpdateScrollMetrics() {
-    assert(SchedulerBinding.instance!.schedulerPhase != SchedulerPhase.persistentCallbacks);
-    if (context.notificationContext != null)
-      ScrollMetricsNotification(metrics: copyWith(), context: context.notificationContext!).dispatch(context.notificationContext);
-  }
-
   /// Provides a heuristic to determine if expensive frame-bound tasks should be
   /// deferred.
   ///
@@ -970,99 +942,3 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
     description.add('viewport: ${_viewportDimension?.toStringAsFixed(1)}');
   }
 }
-
-/// A notification that a scrollable widget's [ScrollMetrics] have changed.
-///
-/// For example, when the content of a scrollable is altered, making it larger
-/// or smaller, this notification will be dispatched. Similarly, if the size
-/// of the window or parent changes, the scrollable can notify of these
-/// changes in dimensions.
-///
-/// The above behaviors usually do not trigger [ScrollNotification] events,
-/// so this is useful for listening to [ScrollMetrics] changes that are not
-/// caused by the user scrolling.
-///
-/// {@tool dartpad --template=freeform}
-/// This sample shows how a [ScrollMetricsNotification] is dispatched when
-/// the `windowSize` is changed. Press the floating action button to increase
-/// the scrollable window's size.
-///
-/// ```dart main
-/// import 'package:flutter/material.dart';
-///
-/// void main() => runApp(const ScrollMetricsDemo());
-///
-/// class ScrollMetricsDemo extends StatefulWidget {
-///   const ScrollMetricsDemo({Key? key}) : super(key: key);
-///
-///   @override
-///   State<ScrollMetricsDemo> createState() => ScrollMetricsDemoState();
-/// }
-///
-/// class ScrollMetricsDemoState extends State<ScrollMetricsDemo> {
-///   double windowSize = 200.0;
-///
-///   @override
-///   Widget build(BuildContext context) {
-///     return MaterialApp(
-///       home: Scaffold(
-///         appBar: AppBar(
-///           title: const Text('ScrollMetrics Demo'),
-///         ),
-///         floatingActionButton: FloatingActionButton(
-///           child: const Icon(Icons.add),
-///           onPressed: () => setState(() {
-///             windowSize += 10.0;
-///           }),
-///         ),
-///         body: NotificationListener<ScrollMetricsNotification>(
-///           onNotification: (ScrollMetricsNotification notification) {
-///             ScaffoldMessenger.of(notification.context).showSnackBar(
-///               const SnackBar(
-///                 content: Text('Scroll metrics changed!'),
-///               ),
-///             );
-///             return false;
-///           },
-///           child: Scrollbar(
-///             isAlwaysShown: true,
-///             child: SizedBox(
-///               height: windowSize,
-///               width: double.infinity,
-///               child: const SingleChildScrollView(
-///                 child: FlutterLogo(
-///                   size: 300.0,
-///                 ),
-///               ),
-///             ),
-///           ),
-///         ),
-///       ),
-///     );
-///   }
-/// }
-/// ```
-/// {@end-tool}
-class ScrollMetricsNotification extends LayoutChangedNotification with ViewportNotificationMixin {
-  /// Creates a notification that the scrollable widget's [ScrollMetrics] have
-  /// changed.
-  ScrollMetricsNotification({
-    required this.metrics,
-    required this.context,
-  });
-
-  /// Description of a scrollable widget's [ScrollMetrics].
-  final ScrollMetrics metrics;
-
-  /// The build context of the widget that fired this notification.
-  ///
-  /// This can be used to find the scrollable widget's render objects to
-  /// determine the size of the viewport, for instance.
-  final BuildContext context;
-
-  @override
-  void debugFillDescription(List<String> description) {
-    super.debugFillDescription(description);
-    description.add('$metrics');
-  }
-}

packages/flutter/test/widgets/scroll_notification_test.dart

@@ -7,64 +7,6 @@ import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  testWidgets('ScrollMetricsNotification test', (WidgetTester tester) async {
-    final List<LayoutChangedNotification> events = <LayoutChangedNotification>[];
-    Widget buildFrame(double height) {
-      return NotificationListener<LayoutChangedNotification>(
-        onNotification: (LayoutChangedNotification value) {
-          events.add(value);
-          return false;
-        },
-        child: SingleChildScrollView(
-          child: SizedBox(height: height),
-        ),
-      );
-    }
-    await tester.pumpWidget(buildFrame(1200.0));
-    // Initial metrics notification.
-    expect(events.length, 1);
-    ScrollMetricsNotification event = events[0] as ScrollMetricsNotification;
-    expect(event.metrics.extentBefore, 0.0);
-    expect(event.metrics.extentInside, 600.0);
-    expect(event.metrics.extentAfter, 600.0);
-
-    events.clear();
-    await tester.pumpWidget(buildFrame(1000.0));
-    // Change the content dimensions will trigger a new event.
-    expect(events.length, 1);
-    event = events[0] as ScrollMetricsNotification;
-    expect(event.metrics.extentBefore, 0.0);
-    expect(event.metrics.extentInside, 600.0);
-    expect(event.metrics.extentAfter, 400.0);
-
-    events.clear();
-    final TestGesture gesture = await tester.startGesture(const Offset(100.0, 100.0));
-    expect(events.length, 1);
-    // user scroll do not trigger the ScrollContentMetricsNotification.
-    expect(events[0] is ScrollStartNotification, true);
-
-    events.clear();
-    await gesture.moveBy(const Offset(-10.0, -10.0));
-    expect(events.length, 2);
-    // User scroll do not trigger the ScrollContentMetricsNotification.
-    expect(events[0] is UserScrollNotification, true);
-    expect(events[1] is ScrollUpdateNotification, true);
-
-    events.clear();
-    // Change the content dimensions again.
-    await tester.pumpWidget(buildFrame(500.0));
-    expect(events.length, 1);
-    event = events[0] as ScrollMetricsNotification;
-    expect(event.metrics.extentBefore, 10.0);
-    expect(event.metrics.extentInside, 590.0);
-    expect(event.metrics.extentAfter, 0.0);
-
-    events.clear();
-    // The content dimensions does not change.
-    await tester.pumpWidget(buildFrame(500.0));
-    expect(events.length, 0);
-  });
-
   testWidgets('Scroll notification basics', (WidgetTester tester) async {
     late ScrollNotification notification;