Add acceptNotification parameter to RefreshIndicator and OverscrollIn… (#12716)

* Add acceptNotification parameter to RefreshIndicator and OverscrollIndicator

* Various fixes suggested by reviewer

* Fixed lint errors

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

@@ -78,7 +78,8 @@ enum _RefreshIndicatorMode {
 class RefreshIndicator extends StatefulWidget {
   /// Creates a refresh indicator.
   ///
-  /// The [onRefresh] and [child] arguments must be non-null. The default
+  /// The [onRefresh], [child], and [notificationPredicate] arguments must be
+  /// non-null. The default
   /// [displacement] is 40.0 logical pixels.
   const RefreshIndicator({
     Key key,
@@ -86,9 +87,11 @@ class RefreshIndicator extends StatefulWidget {
     this.displacement: 40.0,
     @required this.onRefresh,
     this.color,
-    this.backgroundColor
+    this.backgroundColor,
+    this.notificationPredicate: defaultScrollNotificationPredicate,
   }) : assert(child != null),
        assert(onRefresh != null),
+       assert(notificationPredicate != null),
        super(key: key);
 
   /// The refresh indicator will be stacked on top of this child. The indicator
@@ -113,6 +116,13 @@ class RefreshIndicator extends StatefulWidget {
   /// [ThemeData.canvasColor] by default.
   final Color backgroundColor;
   
+  /// A check that specifies whether a [ScrollNotification] should be
+  /// handled by this widget.
+  ///
+  /// By default, checks whether `notification.depth == 0`. Set it to something
+  /// else for more complicated layouts.
+  final ScrollNotificationPredicate notificationPredicate;
+
   @override
   RefreshIndicatorState createState() => new RefreshIndicatorState();
 }
@@ -174,7 +184,7 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
   }
 
   bool _handleScrollNotification(ScrollNotification notification) {
-    if (notification.depth != 0)
+    if (!widget.notificationPredicate(notification))
       return false;
     if (notification is ScrollStartNotification && notification.metrics.extentBefore == 0.0 &&
         _mode == null && _start(notification.metrics.axisDirection)) {

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

@@ -37,19 +37,21 @@ class GlowingOverscrollIndicator extends StatefulWidget {
   /// widget must contain a widget that generates a [ScrollNotification], such
   /// as a [ListView] or a [GridView].
   ///
-  /// The [showLeading], [showTrailing], [axisDirection], and [color] arguments
-  /// must not be null.
+  /// The [showLeading], [showTrailing], [axisDirection], [color], and
+  /// [notificationPredicate] arguments must not be null.
   const GlowingOverscrollIndicator({
     Key key,
     this.showLeading: true,
     this.showTrailing: true,
     @required this.axisDirection,
     @required this.color,
+    this.notificationPredicate: defaultScrollNotificationPredicate,
     this.child,
   }) : assert(showLeading != null),
        assert(showTrailing != null),
        assert(axisDirection != null),
        assert(color != null),
+       assert(notificationPredicate != null),
        super(key: key);
 
   /// Whether to show the overscroll glow on the side with negative scroll
@@ -85,6 +87,13 @@ class GlowingOverscrollIndicator extends StatefulWidget {
   /// The color of the glow. The alpha channel is ignored.
   final Color color;
   
+  /// A check that specifies whether a [ScrollNotification] should be
+  /// handled by this widget.
+  ///
+  /// By default, checks whether `notification.depth == 0`. Set it to something
+  /// else for more complicated layouts.
+  final ScrollNotificationPredicate notificationPredicate;
+
   /// The subtree to place inside the overscroll indicator. This should include
   /// a source of [ScrollNotification] notifications, typically a [Scrollable]
   /// widget.
@@ -144,7 +153,7 @@ class _GlowingOverscrollIndicatorState extends State<GlowingOverscrollIndicator>
   final Map<bool, bool> _accepted = <bool, bool>{false: true, true: true};
 
   bool _handleScrollNotification(ScrollNotification notification) {
-    if (notification.depth != 0)
+    if (!widget.notificationPredicate(notification))
       return false;
     if (notification is OverscrollNotification) {
       _GlowController controller;

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

@@ -282,3 +282,14 @@ class UserScrollNotification extends ScrollNotification {
     description.add('direction: $direction');
   }
 }
+
+/// A predicate for [ScrollNotification], used to customize widgets that
+/// listen to notifications from their children.
+typedef bool ScrollNotificationPredicate(ScrollNotification notification);
+
+/// A [ScrollNotificationPredicate] that checks whether 
+/// `notification.depth == 0`, which means that the notification diid not bubble
+/// through any intervening scrolling widgets.
+bool defaultScrollNotificationPredicate(ScrollNotification notification) {
+  return notification.depth == 0;
+}

packages/flutter/test/material/refresh_indicator_test.dart

@@ -47,6 +47,48 @@ void main() {
     expect(refreshCalled, true);
   });
   
+  testWidgets('Refresh Indicator - nested', (WidgetTester tester) async {
+    refreshCalled = false;
+    await tester.pumpWidget(
+      new MaterialApp(
+        home: new RefreshIndicator(
+          notificationPredicate: (ScrollNotification notification) => notification.depth == 1,
+          onRefresh: refresh,
+          child: new SingleChildScrollView(
+            scrollDirection: Axis.horizontal,
+            child: new Container(
+              width: 600.0,
+              child:new ListView(
+                physics: const AlwaysScrollableScrollPhysics(),
+                children: <String>['A', 'B', 'C', 'D', 'E', 'F'].map((String item) {
+                  return new SizedBox(
+                    height: 200.0,
+                    child: new Text(item),
+                  );
+                }).toList(),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    
+    await tester.fling(find.text('A'), const Offset(300.0, 0.0), 1000.0); // horizontal fling
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1)); // finish the scroll animation
+    await tester.pump(const Duration(seconds: 1)); // finish the indicator settle animation
+    await tester.pump(const Duration(seconds: 1)); // finish the indicator hide animation
+    expect(refreshCalled, false); 
+    
+
+    await tester.fling(find.text('A'), const Offset(0.0, 300.0), 1000.0); // vertical fling
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1)); // finish the scroll animation
+    await tester.pump(const Duration(seconds: 1)); // finish the indicator settle animation
+    await tester.pump(const Duration(seconds: 1)); // finish the indicator hide animation
+    expect(refreshCalled, true); 
+  });
+
   testWidgets('RefreshIndicator - bottom', (WidgetTester tester) async {
     refreshCalled = false;
     await tester.pumpWidget(

packages/flutter/test/widgets/overscroll_indicator_test.dart

@@ -58,6 +58,37 @@ void main() {
     expect(painter, doesNotOverscroll);
   });
   
+  testWidgets('Nested scrollable', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new GlowingOverscrollIndicator(
+          axisDirection: AxisDirection.down,
+          color: const Color(0x0DFFFFFF),
+          notificationPredicate: (ScrollNotification notification) => notification.depth == 1,
+          child: new SingleChildScrollView(
+            scrollDirection: Axis.horizontal,
+            child: new Container(
+                width: 600.0,
+                child: new CustomScrollView(
+                  slivers: <Widget>[
+                      const SliverToBoxAdapter(child: const SizedBox(height: 2000.0)),
+                  ],
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+    
+    final RenderObject outerPainter = tester.renderObject(find.byType(CustomPaint).first);
+    final RenderObject innerPainter = tester.renderObject(find.byType(CustomPaint).last);
+    
+    await slowDrag(tester, const Offset(200.0, 200.0), const Offset(0.0, 5.0));
+    expect(outerPainter, paints..circle());
+    expect(innerPainter, paints..circle());
+  });
+  
   testWidgets('Overscroll indicator changes side when you drag on the other side', (WidgetTester tester) async {
     await tester.pumpWidget(
       new Directionality(