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Avoid divide by zero in scroll thumb rectangle calculations (#10271)

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This commit is contained in:
Jason Simmons 2017-05-24 09:52:09 -07:00 committed by GitHub
parent 251d83a4b5
commit 61e938aa1e
2 changed files with 53 additions and 2 deletions
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9
packages/flutter/lib/src/material/scrollbar.dart
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@ -156,8 +156,13 @@ class _ScrollbarPainter extends ChangeNotifier implements CustomPainter {
void _paintThumb(double before, double inside, double after, double viewport, Canvas canvas, Size size,
void painter(Canvas canvas, Size size, double thumbOffset, double thumbExtent)) {
final double thumbExtent = math.max(math.min(viewport, _kMinThumbExtent), viewport * inside / (before + inside + after));
final double thumbOffset = before * (viewport - thumbExtent) / (before + after);
double thumbExtent = math.min(viewport, _kMinThumbExtent);
if (before + inside + after > 0.0)
thumbExtent = math.max(thumbExtent, viewport * inside / (before + inside + after));
final double thumbOffset = (before + after > 0.0) ?
before * (viewport - thumbExtent) / (before + after) : 0.0;
painter(canvas, size, thumbOffset, thumbExtent);
}

46
packages/flutter/test/material/scrollbar_test.dart
View File

@ -6,6 +6,17 @@ import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter_test/flutter_test.dart';
class TestCanvas implements Canvas {
TestCanvas([this.invocations]);
final List<Invocation> invocations;
@override
void noSuchMethod(Invocation invocation) {
invocations?.add(invocation);
}
}
void main() {
testWidgets('Scrollbar doesn\'t show when tapping list', (WidgetTester tester) async {
await tester.pumpWidget(
@ -48,4 +59,39 @@ void main() {
await tester.pump(const Duration(milliseconds: 200));
await tester.pump(const Duration(milliseconds: 200));
});
testWidgets('ScrollbarPainter does not divide by zero', (WidgetTester tester) async {
await tester.pumpWidget(
new Container(
height: 200.0,
width: 300.0,
child: new Scrollbar(
child: new ListView(
children: <Widget>[
new Container(height: 40.0, child: const Text('0')),
]
)
)
)
);
final CustomPaint custom = tester.widget(find.descendant(of: find.byType(Scrollbar), matching: find.byType(CustomPaint)).first);
final dynamic scrollPainter = custom.foregroundPainter;
final ScrollMetrics metrics = new FixedScrollMetrics(
minScrollExtent: 0.0,
maxScrollExtent: 0.0,
pixels: 0.0,
viewportDimension: 100.0,
axisDirection: AxisDirection.down
);
scrollPainter.update(metrics, AxisDirection.down);
await tester.pump(const Duration(milliseconds: 200));
await tester.pump(const Duration(milliseconds: 200));
final List<Invocation> invocations = <Invocation>[];
final TestCanvas canvas = new TestCanvas(invocations);
scrollPainter.paint(canvas, const Size(10.0, 100.0));
final Rect thumbRect = invocations.single.positionalArguments[0];
expect(thumbRect.isFinite, isTrue);
});
}