ListView.Builder() handles appends when scrolled to the end (#9533)

packages/flutter/lib/src/rendering/sliver_fixed_extent_list.dart

@@ -209,6 +209,10 @@ abstract class RenderSliverFixedExtentBoxAdaptor extends RenderSliverMultiBoxAda
         || constraints.scrollOffset > 0.0,
     );
 
+    // We may have started the layout while scrolled to the end, which would not
+    // expose a new child.
+    if (estimatedMaxScrollOffset == trailingScrollOffset)
+      childManager.setDidUnderflow(true);
     childManager.didFinishLayout();
   }
 }

packages/flutter/lib/src/rendering/sliver_grid.dart

@@ -589,6 +589,10 @@ class RenderSliverGrid extends RenderSliverMultiBoxAdaptor {
       hasVisualOverflow: true,
     );
 
+    // We may have started the layout while scrolled to the end, which
+    // would not expose a new child.
+    if (estimatedTotalExtent == trailingScrollOffset)
+      childManager.setDidUnderflow(true);
     childManager.didFinishLayout();
   }
 }

packages/flutter/lib/src/rendering/sliver_list.dart

@@ -243,6 +243,10 @@ class RenderSliverList extends RenderSliverMultiBoxAdaptor {
       hasVisualOverflow: endScrollOffset > targetEndScrollOffset || constraints.scrollOffset > 0.0,
     );
 
+    // We may have started the layout while scrolled to the end, which would not
+    // expose a new child.
+    if (estimatedMaxScrollOffset == endScrollOffset)
+      childManager.setDidUnderflow(true);
     childManager.didFinishLayout();
   }
 }

packages/flutter/test/widgets/list_view_relayout_test.dart

@@ -124,9 +124,6 @@ void main() {
     expect(find.text('300'), findsOneWidget);
     expect(find.text('400'), findsOneWidget);
     expect(find.text('100'), findsNothing);
-
-    final RenderSliverList list = tester.renderObject(find.byType(SliverList));
-    expect(list.geometry.scrollExtent, equals(700.0));
   });
 
   testWidgets('Overflowing ListView should become scrollable', (WidgetTester tester) async {

packages/flutter/test/widgets/listview_end_append_test.dart

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/widgets.dart';
+
+void main() {
+  testWidgets('ListView.builder() fixed itemExtent, scroll to end, append, scroll', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/9506
+
+    Widget buildFrame(int itemCount) {
+      return new ListView.builder(
+        itemExtent: 200.0,
+        itemCount: itemCount,
+        itemBuilder: (BuildContext context, int index) => new Text('item $index'),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame(3));
+    expect(find.text('item 0'), findsOneWidget);
+    expect(find.text('item 1'), findsOneWidget);
+    expect(find.text('item 2'), findsOneWidget);
+
+    await tester.pumpWidget(buildFrame(4));
+    expect(find.text('item 3'), findsNothing);
+    final TestGesture gesture = await tester.startGesture(const Offset(0.0, 300.0));
+    await gesture.moveBy(const Offset(0.0, -200.0));
+    await tester.pumpAndSettle();
+    expect(find.text('item 3'), findsOneWidget);
+  });
+
+  testWidgets('ListView.builder() fixed itemExtent, scroll to end, append, scroll', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/9506
+
+    Widget buildFrame(int itemCount) {
+      return new ListView.builder(
+        itemCount: itemCount,
+        itemBuilder: (BuildContext context, int index) {
+          return new SizedBox(
+            height: 200.0,
+            child: new Text('item $index'),
+          );
+        },
+      );
+    }
+
+    await tester.pumpWidget(buildFrame(3));
+    expect(find.text('item 0'), findsOneWidget);
+    expect(find.text('item 1'), findsOneWidget);
+    expect(find.text('item 2'), findsOneWidget);
+
+    await tester.pumpWidget(buildFrame(4));
+    final TestGesture gesture = await tester.startGesture(const Offset(0.0, 300.0));
+    await gesture.moveBy(const Offset(0.0, -200.0));
+    await tester.pumpAndSettle();
+    expect(find.text('item 3'), findsOneWidget);
+  });
+}

packages/flutter/test/widgets/scrollable_grid_test.dart

@@ -68,4 +68,31 @@ void main() {
     expect(find.text('3'), findsNothing);
     expect(find.text('4'), findsNothing);
   });
+
+  testWidgets('GridView.count() fixed itemExtent, scroll to end, append, scroll', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/9506
+    Widget buildFrame(int itemCount) {
+      return new GridView.count(
+        crossAxisCount: itemCount,
+        children: new List<Widget>.generate(itemCount, (int index) {
+          return new SizedBox(
+            height: 200.0,
+            child: new Text('item $index'),
+          );
+        }),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame(3));
+    expect(find.text('item 0'), findsOneWidget);
+    expect(find.text('item 1'), findsOneWidget);
+    expect(find.text('item 2'), findsOneWidget);
+
+    await tester.pumpWidget(buildFrame(4));
+    final TestGesture gesture = await tester.startGesture(const Offset(0.0, 300.0));
+    await gesture.moveBy(const Offset(0.0, -200.0));
+    await tester.pumpAndSettle();
+    expect(find.text('item 3'), findsOneWidget);
+  });
+
 }