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showOnScreen doesn't trigger scroll if item is already fully on screen (#17729)

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Michael Goderbauer 2018-05-21 16:33:47 -07:00 committed by GitHub
parent eda3167ac6
commit 7471ff8c89
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4 changed files with 254 additions and 43 deletions
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2
packages/flutter/lib/src/material/app_bar.dart
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@ -920,7 +920,7 @@ class SliverAppBar extends StatefulWidget {
/// Whether the app bar should remain visible at the start of the scroll view.
///
/// The app bar can still expand an contract as the user scrolls, but it will
/// The app bar can still expand and contract as the user scrolls, but it will
/// remain visible rather than being scrolled out of view.
final bool pinned;

71
packages/flutter/lib/src/rendering/viewport.dart
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@ -784,24 +784,65 @@ abstract class RenderViewportBase<ParentDataClass extends ContainerParentDataMix
@override
void showOnScreen([RenderObject child]) {
// Logic duplicated in [_RenderSingleChildViewport.showOnScreen].
if (child != null) {
// TODO(goderbauer): Don't scroll if it is already visible.
// TODO(goderbauer): Don't guess if we need to align at leading or trailing edge.
// Move viewport the smallest distance to bring [child] on screen.
final double leadingEdgeOffset = getOffsetToReveal(child, 0.0);
final double trailingEdgeOffset = getOffsetToReveal(child, 1.0);
final double currentOffset = offset.pixels;
// TODO(goderbauer): Don't scroll if that puts us outside of viewport's bounds.
if ((currentOffset - leadingEdgeOffset).abs() < (currentOffset - trailingEdgeOffset).abs()) {
offset.jumpTo(leadingEdgeOffset);
} else {
offset.jumpTo(trailingEdgeOffset);
}
}
RenderViewportBase.showInViewport(child: child, viewport: this, offset: offset);
// Make sure the viewport itself is on screen.
super.showOnScreen();
}
/// Make the given `child` of the given `viewport` fully visible in the
/// `viewport` by manipulating the provided [ViewportOffset] `offset`.
///
/// The parameters `viewport` and `offset` are required and cannot be null.
/// If `child` is null this is a no-op.
static void showInViewport({
RenderObject child,
@required RenderAbstractViewport viewport,
@required ViewportOffset offset,
}) {
assert(viewport != null);
assert(offset != null);
if (child == null) {
return;
}
final double leadingEdgeOffset = viewport.getOffsetToReveal(child, 0.0);
final double trailingEdgeOffset = viewport.getOffsetToReveal(child, 1.0);
final double currentOffset = offset.pixels;
// scrollOffset
// 0 +---------+
// | |
// _ | |
// viewport position | | |
// with `child` at | | | _
// trailing edge |_ | xxxxxxx | | viewport position
// | | | with `child` at
// | | _| leading edge
// | |
// 800 +---------+
//
// `trailingEdgeOffset`: Distance from scrollOffset 0 to the start of the
// viewport on the left in image above.
// `leadingEdgeOffset`: Distance from scrollOffset 0 to the start of the
// viewport on the right in image above.
//
// The viewport position on the left is achieved by setting `offset.pixels`
// to `trailingEdgeOffset`, the one on the right by setting it to
// `leadingEdgeOffset`.
assert(leadingEdgeOffset >= trailingEdgeOffset);
if (currentOffset > leadingEdgeOffset) {
// `child` currently starts above the leading edge and can be shown fully
// on screen by scrolling down (which means: moving viewport up).
offset.jumpTo(leadingEdgeOffset);
} else if (currentOffset < trailingEdgeOffset ) {
// `child currently ends below the trailing edge and can be shown fully
// on screen by scrolling up (which means: moving viewport down)
offset.jumpTo(trailingEdgeOffset);
}
// else: `child` is between leading and trailing edge and hence already
// fully shown on screen. No action necessary.
}
}
/// A render object that is bigger on the inside.

14
packages/flutter/lib/src/widgets/single_child_scroll_view.dart
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@ -586,19 +586,7 @@ class _RenderSingleChildViewport extends RenderBox with RenderObjectWithChildMix
@override
void showOnScreen([RenderObject child]) {
// Logic duplicated in [RenderViewportBase.showOnScreen].
if (child != null) {
// Move viewport the smallest distance to bring [child] on screen.
final double leadingEdgeOffset = getOffsetToReveal(child, 0.0);
final double trailingEdgeOffset = getOffsetToReveal(child, 1.0);
final double currentOffset = offset.pixels;
if ((currentOffset - leadingEdgeOffset).abs() < (currentOffset - trailingEdgeOffset).abs()) {
offset.jumpTo(leadingEdgeOffset);
} else {
offset.jumpTo(trailingEdgeOffset);
}
}
RenderViewportBase.showInViewport(child: child, viewport: this, offset: offset);
// Make sure the viewport itself is on screen.
super.showOnScreen();
}

210
packages/flutter/test/widgets/scrollable_semantics_test.dart
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@ -137,12 +137,6 @@ void main() {
await tester.pump(const Duration(seconds: 5));
expect(tester.getTopLeft(find.byWidget(containers.first)).dy, kExpandedAppBarHeight);
final int secondContainerId = tester.renderObject(find.byWidget(containers[1])).debugSemantics.id;
tester.binding.pipelineOwner.semanticsOwner.performAction(secondContainerId, SemanticsAction.showOnScreen);
await tester.pump();
await tester.pump(const Duration(seconds: 5));
expect(tester.getTopLeft(find.byWidget(containers[1])).dy, kExpandedAppBarHeight);
semantics.dispose();
});
@ -168,7 +162,7 @@ void main() {
});
final ScrollController scrollController = new ScrollController(
initialScrollOffset: kItemHeight / 2,
initialScrollOffset: 2.5 * kItemHeight,
);
await tester.pumpWidget(new Directionality(
@ -195,7 +189,7 @@ void main() {
),
));
expect(scrollController.offset, kItemHeight / 2);
expect(scrollController.offset, 2.5 * kItemHeight);
final int id0 = tester.renderObject(find.byWidget(children[0])).debugSemantics.id;
tester.binding.pipelineOwner.semanticsOwner.performAction(id0, SemanticsAction.showOnScreen);
@ -203,12 +197,6 @@ void main() {
await tester.pump(const Duration(seconds: 5));
expect(tester.getTopLeft(find.byWidget(children[0])).dy, kToolbarHeight);
final int id1 = tester.renderObject(find.byWidget(children[1])).debugSemantics.id;
tester.binding.pipelineOwner.semanticsOwner.performAction(id1, SemanticsAction.showOnScreen);
await tester.pump();
await tester.pump(const Duration(seconds: 5));
expect(tester.getTopLeft(find.byWidget(children[1])).dy, kToolbarHeight);
semantics.dispose();
});
@ -399,6 +387,200 @@ void main() {
semantics.dispose();
});
group('showOnScreen', () {
const double kItemHeight = 100.0;
List<Widget> children;
ScrollController scrollController;
Widget widgetUnderTest;
setUp(() {
children = new List<Widget>.generate(10, (int i) {
return new MergeSemantics(
child: new Container(
height: kItemHeight,
child: new Text('container $i'),
),
);
});
scrollController = new ScrollController(
initialScrollOffset: kItemHeight / 2,
);
widgetUnderTest = new Directionality(
textDirection: TextDirection.ltr,
child: new Center(
child: new Container(
height: 2 * kItemHeight,
child: new ListView(
controller: scrollController,
children: children,
),
),
),
);
});
testWidgets('brings item above leading edge to leading edge', (WidgetTester tester) async {
semantics = new SemanticsTester(tester); // enables semantics tree generation
await tester.pumpWidget(widgetUnderTest);
expect(scrollController.offset, kItemHeight / 2);
final int firstContainerId = tester.renderObject(find.byWidget(children.first)).debugSemantics.id;
tester.binding.pipelineOwner.semanticsOwner.performAction(firstContainerId, SemanticsAction.showOnScreen);
await tester.pumpAndSettle();
expect(scrollController.offset, 0.0);
semantics.dispose();
});
testWidgets('brings item below trailing edge to trailing edge', (WidgetTester tester) async {
semantics = new SemanticsTester(tester); // enables semantics tree generation
await tester.pumpWidget(widgetUnderTest);
expect(scrollController.offset, kItemHeight / 2);
final int firstContainerId = tester.renderObject(find.byWidget(children[2])).debugSemantics.id;
tester.binding.pipelineOwner.semanticsOwner.performAction(firstContainerId, SemanticsAction.showOnScreen);
await tester.pumpAndSettle();
expect(scrollController.offset, kItemHeight);
semantics.dispose();
});
testWidgets('does not change position of items already fully on-screen', (WidgetTester tester) async {
semantics = new SemanticsTester(tester); // enables semantics tree generation
await tester.pumpWidget(widgetUnderTest);
expect(scrollController.offset, kItemHeight / 2);
final int firstContainerId = tester.renderObject(find.byWidget(children[1])).debugSemantics.id;
tester.binding.pipelineOwner.semanticsOwner.performAction(firstContainerId, SemanticsAction.showOnScreen);
await tester.pumpAndSettle();
expect(scrollController.offset, kItemHeight / 2);
semantics.dispose();
});
});
group('showOnScreen with negative children', () {
const double kItemHeight = 100.0;
List<Widget> children;
ScrollController scrollController;
Widget widgetUnderTest;
setUp(() {
final Key center = new GlobalKey();
children = new List<Widget>.generate(10, (int i) {
return new SliverToBoxAdapter(
key: i == 5 ? center : null,
child: new MergeSemantics(
key: new ValueKey<int>(i),
child: new Container(
height: kItemHeight,
child: new Text('container $i'),
),
),
);
});
scrollController = new ScrollController(
initialScrollOffset: -2.5 * kItemHeight,
);
// 'container 0' is at offset -500
// 'container 1' is at offset -400
// 'container 2' is at offset -300
// 'container 3' is at offset -200
// 'container 4' is at offset -100
// 'container 5' is at offset 0
widgetUnderTest = new Directionality(
textDirection: TextDirection.ltr,
child: new Center(
child: new Container(
height: 2 * kItemHeight,
child: new Scrollable(
controller: scrollController,
viewportBuilder: (BuildContext context, ViewportOffset offset) {
return new Viewport(
cacheExtent: 0.0,
offset: offset,
center: center,
slivers: children
);
},
),
),
),
);
});
testWidgets('brings item above leading edge to leading edge', (WidgetTester tester) async {
semantics = new SemanticsTester(tester); // enables semantics tree generation
await tester.pumpWidget(widgetUnderTest);
expect(scrollController.offset, -250.0);
final int firstContainerId = tester.renderObject(find.byKey(const ValueKey<int>(2))).debugSemantics.id;
tester.binding.pipelineOwner.semanticsOwner.performAction(firstContainerId, SemanticsAction.showOnScreen);
await tester.pumpAndSettle();
expect(scrollController.offset, -300.0);
semantics.dispose();
});
testWidgets('brings item below trailing edge to trailing edge', (WidgetTester tester) async {
semantics = new SemanticsTester(tester); // enables semantics tree generation
await tester.pumpWidget(widgetUnderTest);
expect(scrollController.offset, -250.0);
final int firstContainerId = tester.renderObject(find.byKey(const ValueKey<int>(4))).debugSemantics.id;
tester.binding.pipelineOwner.semanticsOwner.performAction(firstContainerId, SemanticsAction.showOnScreen);
await tester.pumpAndSettle();
expect(scrollController.offset, -200.0);
semantics.dispose();
});
testWidgets('does not change position of items already fully on-screen', (WidgetTester tester) async {
semantics = new SemanticsTester(tester); // enables semantics tree generation
await tester.pumpWidget(widgetUnderTest);
expect(scrollController.offset, -250.0);
final int firstContainerId = tester.renderObject(find.byKey(const ValueKey<int>(3))).debugSemantics.id;
tester.binding.pipelineOwner.semanticsOwner.performAction(firstContainerId, SemanticsAction.showOnScreen);
await tester.pumpAndSettle();
expect(scrollController.offset, -250.0);
semantics.dispose();
});
});
}
Future<Null> flingUp(WidgetTester tester, { int repetitions: 1 }) => fling(tester, const Offset(0.0, -200.0), repetitions);