Created
November 20, 2019 10:21
-
-
Save tomaszpolanski/cf0edb7961d2304c2f293da9971cd4c9 to your computer and use it in GitHub Desktop.
Sliver that scrolls off like SliverPersistentHeader but takes it size from it's child
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
import 'dart:math' as math; | |
import 'package:flutter/rendering.dart'; | |
import 'package:flutter/widgets.dart'; | |
class SliverFloatingHeader extends SingleChildRenderObjectWidget { | |
const SliverFloatingHeader({ | |
Key key, | |
Widget child, | |
}) : super(key: key, child: child); | |
@override | |
RenderSliverFloatingHeader createRenderObject(context) => | |
RenderSliverFloatingHeader(); | |
} | |
class RenderSliverFloatingHeader extends RenderSliverSingleBoxAdapter { | |
RenderSliverFloatingHeader({RenderBox child}) { | |
this.child = child; | |
} | |
double _lastActualScrollOffset; | |
double _effectiveScrollOffset = 0; | |
double _childPosition; | |
@override | |
void performLayout() { | |
if (child == null) { | |
geometry = SliverGeometry.zero; | |
return; | |
} | |
child.layout(constraints.asBoxConstraints(), parentUsesSize: true); | |
final double maxExtent = childExtent; | |
final double paintExtent = maxExtent - (_effectiveScrollOffset ?? 0.0); | |
final double layoutExtent = maxExtent - constraints.scrollOffset; | |
if (_lastActualScrollOffset != null && | |
(constraints.scrollOffset < _lastActualScrollOffset || | |
_effectiveScrollOffset < maxExtent)) { | |
double delta = _lastActualScrollOffset - constraints.scrollOffset; | |
final bool allowFloatingExpansion = | |
constraints.userScrollDirection == ScrollDirection.forward; | |
if (allowFloatingExpansion) { | |
_effectiveScrollOffset = math.min(_effectiveScrollOffset, maxExtent); | |
} else { | |
delta = math.min(delta, 0); | |
} | |
_effectiveScrollOffset = | |
(_effectiveScrollOffset - delta).clamp(0.0, constraints.scrollOffset); | |
} else { | |
_effectiveScrollOffset = constraints.scrollOffset; | |
} | |
excludeFromSemanticsScrolling = | |
_effectiveScrollOffset <= constraints.scrollOffset; | |
geometry = SliverGeometry( | |
scrollExtent: maxExtent, | |
paintOrigin: math.min(constraints.overlap, 0), | |
paintExtent: paintExtent.clamp(0.0, constraints.remainingPaintExtent), | |
layoutExtent: math.min( | |
paintExtent.clamp(0.0, constraints.remainingPaintExtent), | |
layoutExtent.clamp(0.0, constraints.remainingPaintExtent), | |
), | |
maxPaintExtent: maxExtent, | |
hasVisualOverflow: true, | |
); | |
_childPosition = math.min(0, paintExtent - childExtent); | |
_lastActualScrollOffset = constraints.scrollOffset; | |
} | |
double get childExtent { | |
if (child == null) { | |
return 0; | |
} | |
assert(child.hasSize); | |
assert(constraints.axis != null); | |
switch (constraints.axis) { | |
case Axis.vertical: | |
return child.size.height; | |
case Axis.horizontal: | |
return child.size.width; | |
} | |
return null; | |
} | |
@override | |
bool hitTestChildren( | |
SliverHitTestResult result, { | |
@required double mainAxisPosition, | |
@required double crossAxisPosition, | |
}) { | |
assert(geometry.hitTestExtent > 0.0); | |
return child != null && | |
hitTestBoxChild( | |
BoxHitTestResult.wrap(result), | |
child, | |
mainAxisPosition: mainAxisPosition, | |
crossAxisPosition: crossAxisPosition, | |
); | |
} | |
@override | |
void applyPaintTransform(RenderObject child, Matrix4 transform) { | |
assert(child != null); | |
assert(child == this.child); | |
applyPaintTransformForBoxChild(child, transform); | |
} | |
@override | |
void paint(PaintingContext context, Offset offset) { | |
if (child != null && geometry.visible) { | |
assert(constraints.axisDirection != null); | |
switch (applyGrowthDirectionToAxisDirection( | |
constraints.axisDirection, | |
constraints.growthDirection, | |
)) { | |
case AxisDirection.up: | |
offset += Offset( | |
0, | |
geometry.paintExtent - childMainAxisPosition(child) - childExtent, | |
); | |
break; | |
case AxisDirection.down: | |
offset += Offset(0, childMainAxisPosition(child)); | |
break; | |
case AxisDirection.left: | |
offset += Offset( | |
geometry.paintExtent - childMainAxisPosition(child) - childExtent, | |
0, | |
); | |
break; | |
case AxisDirection.right: | |
offset += Offset(childMainAxisPosition(child), 0); | |
break; | |
} | |
context.paintChild(child, offset); | |
} | |
} | |
bool get excludeFromSemanticsScrolling => _excludeFromSemanticsScrolling; | |
bool _excludeFromSemanticsScrolling = false; | |
set excludeFromSemanticsScrolling(bool value) { | |
if (_excludeFromSemanticsScrolling != value) { | |
_excludeFromSemanticsScrolling = value; | |
markNeedsSemanticsUpdate(); | |
} | |
} | |
@override | |
double childMainAxisPosition(RenderBox child) { | |
assert(child == this.child); | |
return _childPosition; | |
} | |
@override | |
void describeSemanticsConfiguration(SemanticsConfiguration config) { | |
super.describeSemanticsConfiguration(config); | |
if (_excludeFromSemanticsScrolling) { | |
config.addTagForChildren(RenderViewport.excludeFromScrolling); | |
} | |
} | |
@override | |
void debugFillProperties(DiagnosticPropertiesBuilder properties) { | |
super.debugFillProperties(properties); | |
properties | |
..add( | |
DoubleProperty('effective scroll offset', _effectiveScrollOffset), | |
) | |
..add( | |
DoubleProperty.lazy( | |
'child position', () => childMainAxisPosition(child)), | |
); | |
} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
null safety support