Add assert for negative child count in ListView.builder (#45506)
diff --git a/packages/flutter/lib/src/widgets/scroll_view.dart b/packages/flutter/lib/src/widgets/scroll_view.dart
index 489fe84..d5a29b9 100644
--- a/packages/flutter/lib/src/widgets/scroll_view.dart
+++ b/packages/flutter/lib/src/widgets/scroll_view.dart
@@ -81,6 +81,7 @@
assert(!shrinkWrap || center == null),
assert(anchor != null),
assert(anchor >= 0.0 && anchor <= 1.0),
+ assert(semanticChildCount == null || semanticChildCount >= 0),
primary = primary ?? controller == null && identical(scrollDirection, Axis.vertical),
physics = physics ?? (primary == true || (primary == null && controller == null && identical(scrollDirection, Axis.vertical)) ? const AlwaysScrollableScrollPhysics() : null),
super(key: key);
@@ -943,7 +944,9 @@
double cacheExtent,
int semanticChildCount,
DragStartBehavior dragStartBehavior = DragStartBehavior.start,
- }) : childrenDelegate = SliverChildBuilderDelegate(
+ }) : assert(itemCount == null || itemCount >= 0),
+ assert(semanticChildCount == null || semanticChildCount <= itemCount),
+ childrenDelegate = SliverChildBuilderDelegate(
itemBuilder,
childCount: itemCount,
addAutomaticKeepAlives: addAutomaticKeepAlives,
diff --git a/packages/flutter/lib/src/widgets/scrollable.dart b/packages/flutter/lib/src/widgets/scrollable.dart
index 179703b..06645fe 100644
--- a/packages/flutter/lib/src/widgets/scrollable.dart
+++ b/packages/flutter/lib/src/widgets/scrollable.dart
@@ -88,6 +88,7 @@
assert(dragStartBehavior != null),
assert(viewportBuilder != null),
assert(excludeFromSemantics != null),
+ assert(semanticChildCount == null || semanticChildCount >= 0),
super (key: key);
/// The direction in which this widget scrolls.
@@ -643,6 +644,7 @@
@required this.semanticChildCount,
Widget child,
}) : assert(position != null),
+ assert(semanticChildCount == null || semanticChildCount >= 0),
super(key: key, child: child);
final ScrollPosition position;
diff --git a/packages/flutter/test/widgets/scroll_view_test.dart b/packages/flutter/test/widgets/scroll_view_test.dart
index 895dfcc..1f866f4 100644
--- a/packages/flutter/test/widgets/scroll_view_test.dart
+++ b/packages/flutter/test/widgets/scroll_view_test.dart
@@ -559,4 +559,33 @@
expect(tester.takeException(), isInstanceOf<Exception>());
expect(finder, findsOneWidget);
});
+
+ testWidgets('ListView.builder asserts on negative childCount', (WidgetTester tester) async {
+ expect(() => ListView.builder(
+ itemBuilder: (BuildContext context, int index) {
+ return const SizedBox();
+ },
+ itemCount: -1,
+ ), throwsA(isInstanceOf<AssertionError>()));
+ });
+
+ testWidgets('ListView.builder asserts on negative semanticChildCount', (WidgetTester tester) async {
+ expect(() => ListView.builder(
+ itemBuilder: (BuildContext context, int index) {
+ return const SizedBox();
+ },
+ itemCount: 1,
+ semanticChildCount: -1,
+ ), throwsA(isInstanceOf<AssertionError>()));
+ });
+
+ testWidgets('ListView.builder asserts on nonsensical childCount/semanticChildCount', (WidgetTester tester) async {
+ expect(() => ListView.builder(
+ itemBuilder: (BuildContext context, int index) {
+ return const SizedBox();
+ },
+ itemCount: 1,
+ semanticChildCount: 4,
+ ), throwsA(isInstanceOf<AssertionError>()));
+ });
}
