Revert "Fix reverse cases for App Bar scrolled under behavior (#101460)" (#101929)

merging now since it blocks flutter roll for too long

packages/flutter/lib/src/material/app_bar.dart

@@ -736,24 +736,24 @@ class _AppBarState extends State<AppBar> {
   static const double _defaultElevation = 4.0;
   static const Color _defaultShadowColor = Color(0xFF000000);
 
-  ScrollMetricsNotificationObserverState? _scrollMetricsNotificationObserver;
+  ScrollNotificationObserverState? _scrollNotificationObserver;
   bool _scrolledUnder = false;
 
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    if (_scrollMetricsNotificationObserver != null)
-      _scrollMetricsNotificationObserver!.removeListener(_handleScrollMetricsNotification);
-    _scrollMetricsNotificationObserver = ScrollMetricsNotificationObserver.of(context);
-    if (_scrollMetricsNotificationObserver != null)
-      _scrollMetricsNotificationObserver!.addListener(_handleScrollMetricsNotification);
+    if (_scrollNotificationObserver != null)
+      _scrollNotificationObserver!.removeListener(_handleScrollNotification);
+    _scrollNotificationObserver = ScrollNotificationObserver.of(context);
+    if (_scrollNotificationObserver != null)
+      _scrollNotificationObserver!.addListener(_handleScrollNotification);
   }
 
   @override
   void dispose() {
-    if (_scrollMetricsNotificationObserver != null) {
-      _scrollMetricsNotificationObserver!.removeListener(_handleScrollMetricsNotification);
-      _scrollMetricsNotificationObserver = null;
+    if (_scrollNotificationObserver != null) {
+      _scrollNotificationObserver!.removeListener(_handleScrollNotification);
+      _scrollNotificationObserver = null;
     }
     super.dispose();
   }
@@ -766,34 +766,18 @@ class _AppBarState extends State<AppBar> {
     Scaffold.of(context).openEndDrawer();
   }
 
-  void _handleScrollMetricsNotification(ScrollMetricsNotification notification) {
-    final bool oldScrolledUnder = _scrolledUnder;
-    final ScrollMetrics metrics = notification.metrics;
-
-    if (notification.depth != 0) {
-      _scrolledUnder = false;
-    } else {
-      switch (metrics.axisDirection) {
-        case AxisDirection.up:
-          // Scroll view is reversed
-          _scrolledUnder = metrics.extentAfter > 0;
-          break;
-        case AxisDirection.down:
-          _scrolledUnder = metrics.extentBefore > 0;
-          break;
-        case AxisDirection.right:
-        case AxisDirection.left:
-        // Scrolled under is only supported in the vertical axis.
-          _scrolledUnder = false;
-          break;
+  void _handleScrollNotification(ScrollNotification notification) {
+    if (notification is ScrollUpdateNotification) {
+      final bool oldScrolledUnder = _scrolledUnder;
+      _scrolledUnder = notification.depth == 0
+          && notification.metrics.extentBefore > 0
+          && notification.metrics.axis == Axis.vertical;
+      if (_scrolledUnder != oldScrolledUnder) {
+        setState(() {
+          // React to a change in MaterialState.scrolledUnder
+        });
       }
     }
-
-    if (_scrolledUnder != oldScrolledUnder) {
-      setState(() {
-        // React to a change in MaterialState.scrolledUnder
-      });
-    }
   }
 
   Color _resolveColor(Set<MaterialState> states, Color? widgetColor, Color? themeColor, Color defaultColor) {

packages/flutter/lib/src/material/scaffold.dart

@@ -2831,7 +2831,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
     return _ScaffoldScope(
       hasDrawer: hasDrawer,
       geometryNotifier: _geometryNotifier,
-      child: ScrollMetricsNotificationObserver(
+      child: ScrollNotificationObserver(
         child: Material(
           color: widget.backgroundColor ?? themeData.scaffoldBackgroundColor,
           child: AnimatedBuilder(animation: _floatingActionButtonMoveController, builder: (BuildContext context, Widget? child) {

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

@@ -9,7 +9,6 @@ import 'package:flutter/foundation.dart';
 import 'framework.dart';
 import 'notification_listener.dart';
 import 'scroll_notification.dart';
-import 'scroll_position.dart';
 
 /// A [ScrollNotification] listener for [ScrollNotificationObserver].
 ///
@@ -171,168 +170,3 @@ class ScrollNotificationObserverState extends State<ScrollNotificationObserver>
     super.dispose();
   }
 }
-
-/// A [ScrollMetricsNotification] listener for [ScrollMetricsNotificationObserver].
-///
-/// [ScrollMetricsNotificationObserver] is similar to
-/// [NotificationListener]. It supports a listener list instead of
-/// just a single listener and its listeners run unconditionally, they
-/// do not require a gating boolean return value.
-typedef ScrollMetricsNotificationCallback = void Function(ScrollMetricsNotification notification);
-
-class _ScrollMetricsNotificationObserverScope extends InheritedWidget {
-  const _ScrollMetricsNotificationObserverScope({
-    required super.child,
-    required ScrollMetricsNotificationObserverState scrollMetricsNotificationObserverState,
-  }) : _scrollMetricsNotificationObserverState = scrollMetricsNotificationObserverState;
-
-  final ScrollMetricsNotificationObserverState  _scrollMetricsNotificationObserverState;
-
-  @override
-  bool updateShouldNotify(_ScrollMetricsNotificationObserverScope old) {
-    return _scrollMetricsNotificationObserverState != old._scrollMetricsNotificationObserverState;
-  }
-}
-
-class _MetricsListenerEntry extends LinkedListEntry<_MetricsListenerEntry> {
-  _MetricsListenerEntry(this.listener);
-  final ScrollMetricsNotificationCallback listener;
-}
-
-/// Notifies its listeners when a descendant ScrollMetrics are
-/// initialized or updated.
-///
-/// To add a listener to a [ScrollMetricsNotificationObserver] ancestor:
-/// ```dart
-/// void listener(ScrollMetricsNotification notification) {
-///   // Do something, maybe setState()
-/// }
-/// ScrollMetricsNotificationObserver.of(context).addListener(listener)
-/// ```
-///
-/// To remove the listener from a [ScrollMetricsNotificationObserver] ancestor:
-/// ```dart
-/// ScrollMetricsNotificationObserver.of(context).removeListener(listener);
-/// ```
-///
-/// Stateful widgets that share an ancestor [ScrollMetricsNotificationObserver]
-/// typically add a listener in [State.didChangeDependencies] (removing the old
-/// one if necessary) and remove the listener in their [State.dispose] method.
-///
-/// This widget is similar to [NotificationListener]. It supports
-/// a listener list instead of just a single listener and its listeners
-/// run unconditionally, they do not require a gating boolean return value.
-class ScrollMetricsNotificationObserver extends StatefulWidget {
-  /// Create a [ScrollMetricsNotificationObserver].
-  ///
-  /// The [child] parameter must not be null.
-  const ScrollMetricsNotificationObserver({
-    super.key,
-    required this.child,
-  }) : assert(child != null);
-
-  /// The subtree below this widget.
-  final Widget child;
-
-  /// The closest instance of this class that encloses the given context.
-  ///
-  /// If there is no enclosing [ScrollMetricsNotificationObserver] widget, then
-  /// null is returned.
-  static ScrollMetricsNotificationObserverState? of(BuildContext context) {
-    return context.dependOnInheritedWidgetOfExactType<_ScrollMetricsNotificationObserverScope>()?._scrollMetricsNotificationObserverState;
-  }
-
-  @override
-  ScrollMetricsNotificationObserverState createState() => ScrollMetricsNotificationObserverState();
-}
-
-/// The listener list state for a [ScrollMetricsNotificationObserver] returned
-/// by [ScrollMetricsNotificationObserver.of].
-///
-/// [ScrollMetricsNotificationObserver] is similar to
-/// [NotificationListener]. It supports a listener list instead of
-/// just a single listener and its listeners run unconditionally, they
-/// do not require a gating boolean return value.
-class ScrollMetricsNotificationObserverState extends State<ScrollMetricsNotificationObserver> {
-  LinkedList<_MetricsListenerEntry>? _listeners = LinkedList<_MetricsListenerEntry>();
-
-  bool _debugAssertNotDisposed() {
-    assert(() {
-      if (_listeners == null) {
-        throw FlutterError(
-          'A $runtimeType was used after being disposed.\n'
-              'Once you have called dispose() on a $runtimeType, it can no longer be used.',
-        );
-      }
-      return true;
-    }());
-    return true;
-  }
-
-  /// Add a [ScrollMetricsNotificationCallback] that will be called each time
-  /// a descendant scrolls.
-  void addListener(ScrollMetricsNotificationCallback listener) {
-    assert(_debugAssertNotDisposed());
-    _listeners!.add(_MetricsListenerEntry(listener));
-  }
-
-  /// Remove the specified [ScrollMetricsNotificationCallback].
-  void removeListener(ScrollMetricsNotificationCallback listener) {
-    assert(_debugAssertNotDisposed());
-    for (final _MetricsListenerEntry entry in _listeners!) {
-      if (entry.listener == listener) {
-        entry.unlink();
-        return;
-      }
-    }
-  }
-
-  void _notifyListeners(ScrollMetricsNotification notification) {
-    assert(_debugAssertNotDisposed());
-    if (_listeners!.isEmpty)
-      return;
-
-    final List<_MetricsListenerEntry> localListeners = List<_MetricsListenerEntry>.of(_listeners!);
-    for (final _MetricsListenerEntry entry in localListeners) {
-      try {
-        if (entry.list != null)
-          entry.listener(notification);
-      } catch (exception, stack) {
-        FlutterError.reportError(FlutterErrorDetails(
-          exception: exception,
-          stack: stack,
-          library: 'widget library',
-          context: ErrorDescription('while dispatching notifications for $runtimeType'),
-          informationCollector: () => <DiagnosticsNode>[
-            DiagnosticsProperty<ScrollMetricsNotificationObserverState>(
-              'The $runtimeType sending notification was',
-              this,
-              style: DiagnosticsTreeStyle.errorProperty,
-            ),
-          ],
-        ));
-      }
-    }
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    return NotificationListener<ScrollMetricsNotification>(
-      onNotification: (ScrollMetricsNotification notification) {
-        _notifyListeners(notification);
-        return false;
-      },
-      child: _ScrollMetricsNotificationObserverScope(
-        scrollMetricsNotificationObserverState: this,
-        child: widget.child,
-      ),
-    );
-  }
-
-  @override
-  void dispose() {
-    assert(_debugAssertNotDisposed());
-    _listeners = null;
-    super.dispose();
-  }
-}

packages/flutter/test/material/debug_test.dart

@@ -344,9 +344,9 @@ void main() {
       '     PhysicalModel\n'
       '     AnimatedPhysicalModel\n'
       '     Material\n'
-      '     _ScrollMetricsNotificationObserverScope\n'
-      '     NotificationListener<ScrollMetricsNotification>\n'
-      '     ScrollMetricsNotificationObserver\n'
+      '     _ScrollNotificationObserverScope\n'
+      '     NotificationListener<ScrollNotification>\n'
+      '     ScrollNotificationObserver\n'
       '     _ScaffoldScope\n'
       '     Scaffold-[LabeledGlobalKey<ScaffoldState>#00000]\n'
       '     MediaQuery\n'

packages/flutter/test/material/scaffold_test.dart

@@ -2302,9 +2302,9 @@ void main() {
       '     PhysicalModel\n'
       '     AnimatedPhysicalModel\n'
       '     Material\n'
-      '     _ScrollMetricsNotificationObserverScope\n'
-      '     NotificationListener<ScrollMetricsNotification>\n'
-      '     ScrollMetricsNotificationObserver\n'
+      '     _ScrollNotificationObserverScope\n'
+      '     NotificationListener<ScrollNotification>\n'
+      '     ScrollNotificationObserver\n'
       '     _ScaffoldScope\n'
       '     Scaffold\n'
       '     MediaQuery\n'