Make disposing a ScrollPosition with pixels=null legal (#44617)
diff --git a/packages/flutter/lib/src/widgets/page_view.dart b/packages/flutter/lib/src/widgets/page_view.dart
index 1e7ab53..9580501 100644
--- a/packages/flutter/lib/src/widgets/page_view.dart
+++ b/packages/flutter/lib/src/widgets/page_view.dart
@@ -333,29 +333,6 @@
final int initialPage;
double _pageToUseOnStartup;
- /// If [pixels] isn't set by [applyViewportDimension] before [dispose] is
- /// called, this could throw an assert as [pixels] will be set to null.
- ///
- /// With [Tab]s, this happens when there are nested [TabBarView]s and there
- /// is an attempt to warp over the nested tab to a tab adjacent to it.
- ///
- /// This flag will be set to true once the dimensions have been established
- /// and [pixels] is set.
- bool isInitialPixelsValueSet = false;
-
- @override
- void dispose() {
- // TODO(shihaohong): remove workaround once these issues have been
- // resolved, https://github.com/flutter/flutter/issues/32054,
- // https://github.com/flutter/flutter/issues/32056
- // Sets `pixels` to a non-null value before `ScrollPosition.dispose` is
- // invoked if it was never set by `applyViewportDimension`.
- if (pixels == null && !isInitialPixelsValueSet) {
- correctPixels(0);
- }
- super.dispose();
- }
-
@override
double get viewportFraction => _viewportFraction;
double _viewportFraction;
@@ -422,7 +399,6 @@
if (newPixels != oldPixels) {
correctPixels(newPixels);
- isInitialPixelsValueSet = true;
return false;
}
return result;
diff --git a/packages/flutter/lib/src/widgets/scroll_position.dart b/packages/flutter/lib/src/widgets/scroll_position.dart
index f1ade32..a661a33 100644
--- a/packages/flutter/lib/src/widgets/scroll_position.dart
+++ b/packages/flutter/lib/src/widgets/scroll_position.dart
@@ -693,7 +693,6 @@
@override
void dispose() {
- assert(pixels != null);
activity?.dispose(); // it will be null if it got absorbed by another ScrollPosition
_activity = null;
super.dispose();
diff --git a/packages/flutter/test/material/tabs_test.dart b/packages/flutter/test/material/tabs_test.dart
index f43a22c..8c2ceef 100644
--- a/packages/flutter/test/material/tabs_test.dart
+++ b/packages/flutter/test/material/tabs_test.dart
@@ -978,8 +978,7 @@
expect(tabController.index, 0);
});
- testWidgets('Nested TabBarView sets ScrollController pixels to non-null value '
- 'when disposed before it is set by the applyViewportDimension', (WidgetTester tester) async {
+ testWidgets('Can switch to non-neighboring tab in nested TabBarView without crashing', (WidgetTester tester) async {
// This is a regression test for https://github.com/flutter/flutter/issues/18756
final TabController _mainTabController = TabController(length: 4, vsync: const TestVSync());
final TabController _nestedTabController = TabController(length: 2, vsync: const TestVSync());
diff --git a/packages/flutter/test/widgets/scrollable_in_overlay_test.dart b/packages/flutter/test/widgets/scrollable_in_overlay_test.dart
new file mode 100644
index 0000000..41e6bad
--- /dev/null
+++ b/packages/flutter/test/widgets/scrollable_in_overlay_test.dart
@@ -0,0 +1,64 @@
+// Copyright 2019 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/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/material.dart';
+
+void main() {
+ test('Can dispose ScrollPosition when pixels is null', () {
+ final ScrollPosition position = ScrollPositionWithSingleContext(
+ initialPixels: null,
+ keepScrollOffset: false,
+ physics: const AlwaysScrollableScrollPhysics(),
+ context: ScrollableState(),
+ );
+
+ expect(position.pixels, isNull);
+ position.dispose(); // Should not throw/assert.
+ });
+
+ testWidgets('scrollable in hidden overlay does not crash when unhidden', (WidgetTester tester) async {
+ // Regression test for https://github.com/flutter/flutter/issues/44269.
+ final TabController controller = TabController(vsync: const TestVSync(), length: 1);
+
+ final OverlayEntry entry1 = OverlayEntry(
+ maintainState: true,
+ opaque: true,
+ builder: (BuildContext context) {
+ return TabBar(
+ isScrollable: true,
+ controller: controller,
+ tabs: const <Tab>[
+ Tab(text: 'Main'),
+ ],
+ );
+ },
+ );
+ final OverlayEntry entry2 = OverlayEntry(
+ maintainState: true,
+ opaque: true,
+ builder: (BuildContext context) {
+ return const Text('number2');
+ },
+ );
+
+ await tester.pumpWidget(
+ MaterialApp(
+ home: Material(
+ child: Overlay(
+ initialEntries: <OverlayEntry>[
+ entry1,
+ entry2,
+ ],
+ ),
+ ),
+ ),
+ );
+
+ entry2.remove();
+ await tester.pump();
+ expect(tester.takeException(), isNull);
+ });
+}
