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DecoratedSliver (#127823)
This is a second attempt to merge #107269. Currently I've fixed two of the issues: 1. Fixed horizontal scrollview by using a switch statement to consider vertical/horizontal case. 2. Fixed issue of `paintExtent` not being the right extent for painting. Rather using a `scrollExtent` for the main axis length of the decoration box and painting it offsetted by the `scrollOffset`. 3. If the sliver child has inifinite scrollExtent, then we only draw the decoration down to the bottom of the `cacheExtent`. The developer is expected to ensure that the border does not creep up above the cache area. This PR includes a test that checks that the correct rectangle is drawn at a certain scrollOffset for both the horizontal and vertical case which should be sufficient for checking that `SliverDecoration` works properly now. Fixes flutter/flutter#107498.
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‎examples/api/lib/widgets/sliver/decorated_sliver.0.dart

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// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'package:flutter/material.dart';
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void main() => runApp(const SliverDecorationExampleApp());
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class SliverDecorationExampleApp extends StatelessWidget {
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const SliverDecorationExampleApp({super.key});
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@override
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Widget build(BuildContext context) {
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return MaterialApp(
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home: Scaffold(
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appBar: AppBar(title: const Text('SliverDecoration Sample')),
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body: const SliverDecorationExample(),
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),
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);
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}
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}
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class SliverDecorationExample extends StatelessWidget {
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const SliverDecorationExample({super.key});
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@override
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Widget build(BuildContext context) {
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return CustomScrollView(
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slivers: <Widget>[
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DecoratedSliver(
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decoration: const BoxDecoration(
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gradient: RadialGradient(
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center: Alignment(-0.5, -0.6),
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radius: 0.15,
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colors: <Color>[
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Color(0xFFEEEEEE),
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Color(0xFF111133),
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],
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stops: <double>[0.9, 1.0],
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),
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),
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sliver: SliverList(
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delegate: SliverChildListDelegate(<Widget>[
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const Text('Goodnight Moon'),
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]),
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),
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),
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const DecoratedSliver(
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decoration: BoxDecoration(
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color: Colors.amber,
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borderRadius: BorderRadius.all(Radius.circular(50))
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),
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sliver: SliverToBoxAdapter(child: SizedBox(height: 300)),
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),
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],
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);
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}
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}

‎packages/flutter/lib/rendering.dart

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export 'src/rendering/custom_paint.dart';
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export 'src/rendering/debug.dart';
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export 'src/rendering/debug_overflow_indicator.dart';
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export 'src/rendering/decorated_sliver.dart';
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export 'src/rendering/editable.dart';
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export 'src/rendering/error.dart';
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export 'src/rendering/flex.dart';

‎packages/flutter/lib/src/painting/box_decoration.dart

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///
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/// * [DecoratedBox] and [Container], widgets that can be configured with
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/// [BoxDecoration] objects.
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/// * [DecoratedSliver], a widget that can be configured with a [BoxDecoration]
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/// that is converted to render with slivers.
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/// * [CustomPaint], a widget that lets you draw arbitrary graphics.
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/// * [Decoration], the base class which lets you define other decorations.
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class BoxDecoration extends Decoration {

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

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// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'object.dart';
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import 'proxy_box.dart';
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import 'proxy_sliver.dart';
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import 'sliver.dart';
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/// Paints a [Decoration] either before or after its child paints.
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///
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/// If the child has infinite scroll extent, then the [Decoration] paints itself up to the
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/// bottom cache extent.
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class RenderDecoratedSliver extends RenderProxySliver {
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/// Creates a decorated sliver.
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///
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/// The [decoration], [position], and [configuration] arguments must not be
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/// null. By default the decoration paints behind the child.
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///
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/// The [ImageConfiguration] will be passed to the decoration (with the size
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/// filled in) to let it resolve images.
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RenderDecoratedSliver({
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required Decoration decoration,
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DecorationPosition position = DecorationPosition.background,
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ImageConfiguration configuration = ImageConfiguration.empty,
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}) : _decoration = decoration,
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_position = position,
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_configuration = configuration;
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/// What decoration to paint.
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///
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/// Commonly a [BoxDecoration].
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Decoration get decoration => _decoration;
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Decoration _decoration;
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set decoration(Decoration value) {
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if (value == decoration) {
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return;
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}
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_decoration = value;
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_painter?.dispose();
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_painter = decoration.createBoxPainter(markNeedsPaint);
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markNeedsPaint();
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}
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/// Whether to paint the box decoration behind or in front of the child.
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DecorationPosition get position => _position;
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DecorationPosition _position;
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set position(DecorationPosition value) {
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if (value == position) {
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return;
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}
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_position = value;
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markNeedsPaint();
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}
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/// The settings to pass to the decoration when painting, so that it can
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/// resolve images appropriately. See [ImageProvider.resolve] and
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/// [BoxPainter.paint].
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///
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/// The [ImageConfiguration.textDirection] field is also used by
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/// direction-sensitive [Decoration]s for painting and hit-testing.
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ImageConfiguration get configuration => _configuration;
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ImageConfiguration _configuration;
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set configuration(ImageConfiguration value) {
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if (value == configuration) {
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return;
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}
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_configuration = value;
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markNeedsPaint();
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}
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BoxPainter? _painter;
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@override
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void attach(covariant PipelineOwner owner) {
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_painter = decoration.createBoxPainter(markNeedsPaint);
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super.attach(owner);
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}
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@override
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void detach() {
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_painter?.dispose();
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_painter = null;
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super.detach();
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}
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@override
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void dispose() {
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_painter?.dispose();
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_painter = null;
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super.dispose();
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}
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@override
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void paint(PaintingContext context, Offset offset) {
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if (child != null && child!.geometry!.visible) {
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final SliverPhysicalParentData childParentData = child!.parentData! as SliverPhysicalParentData;
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final Size childSize;
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final Offset scrollOffset;
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// In the case where the child sliver has infinite scroll extent, the decoration
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// should only extend down to the bottom cache extent.
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final double cappedMainAxisExtent = child!.geometry!.scrollExtent.isInfinite
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? constraints.scrollOffset + child!.geometry!.cacheExtent + constraints.cacheOrigin
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: child!.geometry!.scrollExtent;
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switch (constraints.axis) {
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case Axis.vertical:
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childSize = Size(constraints.crossAxisExtent, cappedMainAxisExtent);
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scrollOffset = Offset(0.0, -constraints.scrollOffset);
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case Axis.horizontal:
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childSize = Size(cappedMainAxisExtent, constraints.crossAxisExtent);
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scrollOffset = Offset(-constraints.scrollOffset, 0.0);
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}
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final Offset childOffset = offset + childParentData.paintOffset;
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if (position == DecorationPosition.background) {
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_painter!.paint(context.canvas, childOffset + scrollOffset, configuration.copyWith(size: childSize));
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}
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context.paintChild(child!, childOffset);
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if (position == DecorationPosition.foreground) {
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_painter!.paint(context.canvas, childOffset + scrollOffset, configuration.copyWith(size: childSize));
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}
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}
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}
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}

‎packages/flutter/lib/src/widgets/container.dart

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/// * [Decoration], which you can extend to provide other effects with
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/// [DecoratedBox].
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/// * [CustomPaint], another way to draw custom effects from the widget layer.
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/// * [DecoratedSliver], which applies a [Decoration] to a sliver.
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class DecoratedBox extends SingleChildRenderObjectWidget {
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/// Creates a widget that paints a [Decoration].
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///

‎packages/flutter/lib/src/widgets/decorated_sliver.dart

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// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'package:flutter/rendering.dart';
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import 'basic.dart';
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import 'framework.dart';
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import 'image.dart';
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/// A sliver widget that paints a [Decoration] either before or after its child
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/// paints.
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///
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/// Unlike [DecoratedBox], this widget expects its child to be a sliver, and
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/// must be placed in a widget that expects a sliver.
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///
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/// If the child sliver has infinite [SliverGeometry.scrollExtent], then we only
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/// draw the decoration down to the bottom [SliverGeometry.cacheExtent], and
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/// it is necessary to ensure that the bottom border does not creep
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/// above the top of the bottom cache. This can happen if the bottom has a
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/// border radius larger than the extent of the cache area.
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///
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/// Commonly used with [BoxDecoration].
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///
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/// The [child] is not clipped. To clip a child to the shape of a particular
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/// [ShapeDecoration], consider using a [ClipPath] widget.
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///
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/// {@tool dartpad}
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/// This sample shows a radial gradient that draws a moon on a night sky:
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///
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/// ** See code in examples/api/lib/widgets/sliver/decorated_sliver.0.dart **
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/// {@end-tool}
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///
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/// See also:
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///
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/// * [DecoratedBox], the version of this class that works with RenderBox widgets.
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/// * [Decoration], which you can extend to provide other effects with
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/// [DecoratedSliver].
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/// * [CustomPaint], another way to draw custom effects from the widget layer.
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class DecoratedSliver extends SingleChildRenderObjectWidget {
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/// Creates a widget that paints a [Decoration].
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///
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/// The [decoration] and [position] arguments must not be null. By default the
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/// decoration paints behind the child.
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const DecoratedSliver({
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super.key,
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required this.decoration,
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this.position = DecorationPosition.background,
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Widget? sliver,
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}) : super(child: sliver);
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/// What decoration to paint.
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///
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/// Commonly a [BoxDecoration].
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final Decoration decoration;
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/// Whether to paint the box decoration behind or in front of the child.
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final DecorationPosition position;
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@override
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RenderDecoratedSliver createRenderObject(BuildContext context) {
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return RenderDecoratedSliver(
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decoration: decoration,
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position: position,
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configuration: createLocalImageConfiguration(context),
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);
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}
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@override
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void updateRenderObject(BuildContext context, RenderDecoratedSliver renderObject) {
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renderObject
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..decoration = decoration
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..position = position
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..configuration = createLocalImageConfiguration(context);
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}
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@override
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void debugFillProperties(DiagnosticPropertiesBuilder properties) {
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super.debugFillProperties(properties);
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final String label;
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switch (position) {
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case DecorationPosition.background:
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label = 'bg';
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case DecorationPosition.foreground:
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label = 'fg';
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}
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properties.add(EnumProperty<DecorationPosition>('position', position, level: DiagnosticLevel.hidden));
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properties.add(DiagnosticsProperty<Decoration>(label, decoration));
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}
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}

‎packages/flutter/lib/widgets.dart

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export 'src/widgets/context_menu_button_item.dart';
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export 'src/widgets/context_menu_controller.dart';
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export 'src/widgets/debug.dart';
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export 'src/widgets/decorated_sliver.dart';
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export 'src/widgets/default_selection_style.dart';
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export 'src/widgets/default_text_editing_shortcuts.dart';
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export 'src/widgets/desktop_text_selection_toolbar_layout_delegate.dart';

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