SliverAppBar
- expandedHeight
This does not include the status bar height (which will be automatically included if [primary] is true).
The height of the merge, default is the height of the status bar plus the height of the AppBar
[primary]:trueCopy the code- backgroundColor
Background color (folded background color is also this property)
- leading
The icon or text on the left is usually a return arrow
- automaticallyImplyLeading
When leading is not true, the arrow is returned by default
If there is no leading and it is false, title is displayed
| leading | automaticallyImplyLeading | result |
|---|---|---|
| null | true | Returns the arrow |
| null | false | Instead of returning the arrow, display the title if there is one |
| not null | true | invalid |
| not null | false | invalid |
- title
The title
- actions
The operation to the right of the title
- primary
False takes the height of the status bar if it is displayed below it
- centerTitle
Whether the title is centered
- pinned
Whether the title bar is fixed
- elevation
Size of the shadow
- forceElevated
Whether to show shadows
- brightness
Status bar subject color
- titleSpacing
The title spacing
- flexibleSpace(*)
Background content area of SliverAppBar, usually using FlexibleSpaceBar
- collapsedHeight
Height after folding The height of the default toolbarHeight
- floating
No pull-down occurs and SliverAppBar immediately appears
- snap
Must be used in conjunction with floating:true to indicate whether the SliverAppBar will fully unfold if it is not fully stretched after it is displayed
- stretch
Look at this wow, the explanation is in place, graphic, medium.com/flutter-com…
FlexibleSpaceBar
- collapseMode
Collapsemode. pin: Scroll together until collapse
CollapseMode. Parallax: Visual gradation, more obvious drawer effect
- stretchModes
StretchMode. ZoomBackground – > background widget will expand to fill the additional space.
StretchMode. BlurBackground – > use ImageFilter. The blur effect, the background will be blurred.
Stretchmodetitle – > Title will disappear as the user overscrolls.
Custom SliverAppBar, implement appBar title only in fully collapsed state display
- The key code
bool _verticalOffsetZero = false; AppBarStateChangeController _appBarStateChangeController = AppBarStateChangeController(); _appBarStateChangeController.addListener(() { var verticalOffsetZero = _appBarStateChangeController.verticalOffsetZero; if (_verticalOffsetZero ! = verticalOffsetZero) { logger("verticalOffsetZero >>> $verticalOffsetZero"); WidgetsBinding.instance? .addPostFramecallBack ((_) {// The widget that needs to be created setState(() {}); }); } _verticalOffsetZero = verticalOffsetZero; }); MySliverAppBar( appBarStateChangeController: _appBarStateChangeController, )Copy the code- MySliverAppBar section (copy the SliverAppBar completely and change it, if you don’t have my requirement, SliverAppBar is still recommended)
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'dart:math' as math;
class MySliverAppBar extends StatefulWidget {
/// Creates a material design app bar that can be placed in a [CustomScrollView].
///
/// The arguments [forceElevated], [primary], [floating], [pinned], [snap]
/// and [automaticallyImplyLeading] must not be null.
const MySliverAppBar({
Key? key,
this.leading,
this.automaticallyImplyLeading = true,
this.title,
this.actions,
this.flexibleSpace,
this.bottom,
this.elevation,
this.shadowColor,
this.forceElevated = false,
this.backgroundColor,
this.foregroundColor,
this.brightness,
this.iconTheme,
this.actionsIconTheme,
this.textTheme,
this.primary = true,
this.centerTitle,
this.excludeHeaderSemantics = false,
this.titleSpacing,
this.collapsedHeight,
this.expandedHeight,
this.floating = false,
this.pinned = false,
this.snap = false,
this.stretch = false,
this.stretchTriggerOffset = 100.0,
this.onStretchTrigger,
this.shape,
this.toolbarHeight = kToolbarHeight,
this.leadingWidth,
this.backwardsCompatibility,
this.toolbarTextStyle,
this.titleTextStyle,
this.systemOverlayStyle,
this.appBarStateChangeController,
}) : assert(automaticallyImplyLeading != null),
assert(forceElevated != null),
assert(primary != null),
assert(floating != null),
assert(pinned != null),
assert(snap != null),
assert(stretch != null),
assert(toolbarHeight != null),
assert(floating || !snap,
'The "snap" argument only makes sense for floating app bars.'),
assert(stretchTriggerOffset > 0.0),
assert(collapsedHeight == null || collapsedHeight >= toolbarHeight,
'The "collapsedHeight" argument has to be larger than or equal to [toolbarHeight].'),
super(key: key);
/// {@macro flutter.material.appbar.leading}
///
/// This property is used to configure an [AppBar].
final Widget? leading;
/// 监听app bar 高度变化，custom熟悉
final AppBarStateChangeController? appBarStateChangeController;
/// {@macro flutter.material.appbar.automaticallyImplyLeading}
///
/// This property is used to configure an [AppBar].
final bool automaticallyImplyLeading;
/// {@macro flutter.material.appbar.title}
///
/// This property is used to configure an [AppBar].
final Widget? title;
/// {@macro flutter.material.appbar.actions}
///
/// This property is used to configure an [AppBar].
final List<Widget>? actions;
/// {@macro flutter.material.appbar.flexibleSpace}
///
/// This property is used to configure an [AppBar].
final Widget? flexibleSpace;
/// {@macro flutter.material.appbar.bottom}
///
/// This property is used to configure an [AppBar].
final PreferredSizeWidget? bottom;
/// {@macro flutter.material.appbar.elevation}
///
/// This property is used to configure an [AppBar].
final double? elevation;
/// {@macro flutter.material.appbar.shadowColor}
///
/// This property is used to configure an [AppBar].
final Color? shadowColor;
/// Whether to show the shadow appropriate for the [elevation] even if the
/// content is not scrolled under the [AppBar].
///
/// Defaults to false, meaning that the [elevation] is only applied when the
/// [AppBar] is being displayed over content that is scrolled under it.
///
/// When set to true, the [elevation] is applied regardless.
///
/// Ignored when [elevation] is zero.
final bool forceElevated;
/// {@macro flutter.material.appbar.backgroundColor}
///
/// This property is used to configure an [AppBar].
final Color? backgroundColor;
/// {@macro flutter.material.appbar.foregroundColor}
///
/// This property is used to configure an [AppBar].
final Color? foregroundColor;
/// {@macro flutter.material.appbar.brightness}
///
/// This property is used to configure an [AppBar].
final Brightness? brightness;
/// {@macro flutter.material.appbar.iconTheme}
///
/// This property is used to configure an [AppBar].
final IconThemeData? iconTheme;
/// {@macro flutter.material.appbar.actionsIconTheme}
///
/// This property is used to configure an [AppBar].
final IconThemeData? actionsIconTheme;
/// {@macro flutter.material.appbar.textTheme}
///
/// This property is used to configure an [AppBar].
final TextTheme? textTheme;
/// {@macro flutter.material.appbar.primary}
///
/// This property is used to configure an [AppBar].
final bool primary;
/// {@macro flutter.material.appbar.centerTitle}
///
/// This property is used to configure an [AppBar].
final bool? centerTitle;
/// {@macro flutter.material.appbar.excludeHeaderSemantics}
///
/// This property is used to configure an [AppBar].
final bool excludeHeaderSemantics;
/// {@macro flutter.material.appbar.titleSpacing}
///
/// This property is used to configure an [AppBar].
final double? titleSpacing;
/// Defines the height of the app bar when it is collapsed.
///
/// By default, the collapsed height is [toolbarHeight]. If [bottom] widget is
/// specified, then its height from [PreferredSizeWidget.preferredSize] is
/// added to the height. If [primary] is true, then the [MediaQuery] top
/// padding, [EdgeInsets.top] of [MediaQueryData.padding], is added as well.
///
/// If [pinned] and [floating] are true, with [bottom] set, the default
/// collapsed height is only the height of [PreferredSizeWidget.preferredSize]
/// with the [MediaQuery] top padding.
final double? collapsedHeight;
/// The size of the app bar when it is fully expanded.
///
/// By default, the total height of the toolbar and the bottom widget (if
/// any). If a [flexibleSpace] widget is specified this height should be big
/// enough to accommodate whatever that widget contains.
///
/// This does not include the status bar height (which will be automatically
/// included if [primary] is true).
final double? expandedHeight;
/// Whether the app bar should become visible as soon as the user scrolls
/// towards the app bar.
///
/// Otherwise, the user will need to scroll near the top of the scroll view to
/// reveal the app bar.
///
/// If [snap] is true then a scroll that exposes the app bar will trigger an
/// animation that slides the entire app bar into view. Similarly if a scroll
/// dismisses the app bar, the animation will slide it completely out of view.
///
/// ## Animated Examples
///
/// The following animations show how the app bar changes its scrolling
/// behavior based on the value of this property.
///
/// * App bar with [floating] set to false:
/// {@animation 476 400 https://flutter.github.io/assets-for-api-docs/assets/material/app_bar.mp4}
/// * App bar with [floating] set to true:
/// {@animation 476 400 https://flutter.github.io/assets-for-api-docs/assets/material/app_bar_floating.mp4}
///
/// See also:
///
/// * [MySliverAppBar] for more animated examples of how this property changes the
/// behavior of the app bar in combination with [pinned] and [snap].
final bool floating;
/// Whether the app bar should remain visible at the start of the scroll view.
///
/// The app bar can still expand and contract as the user scrolls, but it will
/// remain visible rather than being scrolled out of view.
///
/// ## Animated Examples
///
/// The following animations show how the app bar changes its scrolling
/// behavior based on the value of this property.
///
/// * App bar with [pinned] set to false:
/// {@animation 476 400 https://flutter.github.io/assets-for-api-docs/assets/material/app_bar.mp4}
/// * App bar with [pinned] set to true:
/// {@animation 476 400 https://flutter.github.io/assets-for-api-docs/assets/material/app_bar_pinned.mp4}
///
/// See also:
///
/// * [MySliverAppBar] for more animated examples of how this property changes the
/// behavior of the app bar in combination with [floating].
final bool pinned;
/// {@macro flutter.material.appbar.shape}
///
/// This property is used to configure an [AppBar].
final ShapeBorder? shape;
/// If [snap] and [floating] are true then the floating app bar will "snap"
/// into view.
///
/// If [snap] is true then a scroll that exposes the floating app bar will
/// trigger an animation that slides the entire app bar into view. Similarly
/// if a scroll dismisses the app bar, the animation will slide the app bar
/// completely out of view. Additionally, setting [snap] to true will fully
/// expand the floating app bar when the framework tries to reveal the
/// contents of the app bar by calling [RenderObject.showOnScreen]. For
/// example, when a [TextField] in the floating app bar gains focus, if [snap]
/// is true, the framework will always fully expand the floating app bar, in
/// order to reveal the focused [TextField].
///
/// Snapping only applies when the app bar is floating, not when the app bar
/// appears at the top of its scroll view.
///
/// ## Animated Examples
///
/// The following animations show how the app bar changes its scrolling
/// behavior based on the value of this property.
///
/// * App bar with [snap] set to false:
/// {@animation 476 400 https://flutter.github.io/assets-for-api-docs/assets/material/app_bar_floating.mp4}
/// * App bar with [snap] set to true:
/// {@animation 476 400 https://flutter.github.io/assets-for-api-docs/assets/material/app_bar_floating_snap.mp4}
///
/// See also:
///
/// * [MySliverAppBar] for more animated examples of how this property changes the
/// behavior of the app bar in combination with [pinned] and [floating].
final bool snap;
/// Whether the app bar should stretch to fill the over-scroll area.
///
/// The app bar can still expand and contract as the user scrolls, but it will
/// also stretch when the user over-scrolls.
final bool stretch;
/// The offset of overscroll required to activate [onStretchTrigger].
///
/// This defaults to 100.0.
final double stretchTriggerOffset;
/// The callback function to be executed when a user over-scrolls to the
/// offset specified by [stretchTriggerOffset].
final AsyncCallback? onStretchTrigger;
/// {@macro flutter.material.appbar.toolbarHeight}
///
/// This property is used to configure an [AppBar].
final double toolbarHeight;
/// {@macro flutter.material.appbar.leadingWidth}
///
/// This property is used to configure an [AppBar].
final double? leadingWidth;
/// {@macro flutter.material.appbar.backwardsCompatibility}
///
/// This property is used to configure an [AppBar].
final bool? backwardsCompatibility;
/// {@macro flutter.material.appbar.toolbarTextStyle}
///
/// This property is used to configure an [AppBar].
final TextStyle? toolbarTextStyle;
/// {@macro flutter.material.appbar.titleTextStyle}
///
/// This property is used to configure an [AppBar].
final TextStyle? titleTextStyle;
/// {@macro flutter.material.appbar.systemOverlayStyle}
///
/// This property is used to configure an [AppBar].
final SystemUiOverlayStyle? systemOverlayStyle;
@override
_MySliverAppBarState createState() => _MySliverAppBarState();
}
// This class is only Stateful because it owns the TickerProvider used
// by the floating appbar snap animation (via FloatingHeaderSnapConfiguration).
class _MySliverAppBarState extends State<MySliverAppBar>
with TickerProviderStateMixin {
FloatingHeaderSnapConfiguration? _snapConfiguration;
OverScrollHeaderStretchConfiguration? _stretchConfiguration;
PersistentHeaderShowOnScreenConfiguration? _showOnScreenConfiguration;
void _updateSnapConfiguration() {
if (widget.snap && widget.floating) {
_snapConfiguration = FloatingHeaderSnapConfiguration(
curve: Curves.easeOut,
duration: const Duration(milliseconds: 200),
);
} else {
_snapConfiguration = null;
}
_showOnScreenConfiguration = widget.floating & widget.snap
? const PersistentHeaderShowOnScreenConfiguration(
minShowOnScreenExtent: double.infinity)
: null;
}
void _updateStretchConfiguration() {
if (widget.stretch) {
_stretchConfiguration = OverScrollHeaderStretchConfiguration(
stretchTriggerOffset: widget.stretchTriggerOffset,
onStretchTrigger: widget.onStretchTrigger,
);
} else {
_stretchConfiguration = null;
}
}
@override
void initState() {
super.initState();
_updateSnapConfiguration();
_updateStretchConfiguration();
}
@override
void didUpdateWidget(MySliverAppBar oldWidget) {
super.didUpdateWidget(oldWidget);
if (widget.snap != oldWidget.snap || widget.floating != oldWidget.floating)
_updateSnapConfiguration();
if (widget.stretch != oldWidget.stretch) _updateStretchConfiguration();
}
@override
Widget build(BuildContext context) {
assert(!widget.primary || debugCheckHasMediaQuery(context));
final double bottomHeight = widget.bottom?.preferredSize.height ?? 0.0;
final double topPadding =
widget.primary ? MediaQuery.of(context).padding.top : 0.0;
final double collapsedHeight =
(widget.pinned && widget.floating && widget.bottom != null)
? (widget.collapsedHeight ?? 0.0) + bottomHeight + topPadding
: (widget.collapsedHeight ?? widget.toolbarHeight) +
bottomHeight +
topPadding;
return MediaQuery.removePadding(
context: context,
removeBottom: true,
child: SliverPersistentHeader(
floating: widget.floating,
pinned: widget.pinned,
delegate: _SliverAppBarDelegate(
vsync: this,
leading: widget.leading,
appBarStateChangeController: widget.appBarStateChangeController,
automaticallyImplyLeading: widget.automaticallyImplyLeading,
title: widget.title,
actions: widget.actions,
flexibleSpace: widget.flexibleSpace,
bottom: widget.bottom,
elevation: widget.elevation,
shadowColor: widget.shadowColor,
forceElevated: widget.forceElevated,
backgroundColor: widget.backgroundColor,
foregroundColor: widget.foregroundColor,
brightness: widget.brightness,
iconTheme: widget.iconTheme,
actionsIconTheme: widget.actionsIconTheme,
textTheme: widget.textTheme,
primary: widget.primary,
centerTitle: widget.centerTitle,
excludeHeaderSemantics: widget.excludeHeaderSemantics,
titleSpacing: widget.titleSpacing,
expandedHeight: widget.expandedHeight,
collapsedHeight: collapsedHeight,
topPadding: topPadding,
floating: widget.floating,
pinned: widget.pinned,
shape: widget.shape,
snapConfiguration: _snapConfiguration,
stretchConfiguration: _stretchConfiguration,
showOnScreenConfiguration: _showOnScreenConfiguration,
toolbarHeight: widget.toolbarHeight,
leadingWidth: widget.leadingWidth,
backwardsCompatibility: widget.backwardsCompatibility,
toolbarTextStyle: widget.toolbarTextStyle,
titleTextStyle: widget.titleTextStyle,
systemOverlayStyle: widget.systemOverlayStyle,
),
),
);
}
}
class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
_SliverAppBarDelegate({
required this.leading,
required this.automaticallyImplyLeading,
required this.title,
required this.actions,
required this.flexibleSpace,
required this.bottom,
required this.elevation,
required this.shadowColor,
required this.forceElevated,
required this.backgroundColor,
required this.foregroundColor,
required this.brightness,
required this.iconTheme,
required this.actionsIconTheme,
required this.textTheme,
required this.primary,
required this.centerTitle,
required this.excludeHeaderSemantics,
required this.titleSpacing,
required this.expandedHeight,
required this.collapsedHeight,
required this.topPadding,
required this.floating,
required this.pinned,
required this.vsync,
required this.snapConfiguration,
required this.stretchConfiguration,
required this.showOnScreenConfiguration,
required this.shape,
required this.toolbarHeight,
required this.leadingWidth,
required this.backwardsCompatibility,
required this.toolbarTextStyle,
required this.titleTextStyle,
required this.systemOverlayStyle,
required this.appBarStateChangeController,
}) : assert(primary || topPadding == 0.0),
assert(
!floating ||
(snapConfiguration == null &&
showOnScreenConfiguration == null) ||
vsync != null,
'vsync cannot be null when snapConfiguration or showOnScreenConfiguration is not null, and floating is true',
),
_bottomHeight = bottom?.preferredSize.height ?? 0.0;
final Widget? leading;
final AppBarStateChangeController? appBarStateChangeController;
final bool automaticallyImplyLeading;
final Widget? title;
final List<Widget>? actions;
final Widget? flexibleSpace;
final PreferredSizeWidget? bottom;
final double? elevation;
final Color? shadowColor;
final bool forceElevated;
final Color? backgroundColor;
final Color? foregroundColor;
final Brightness? brightness;
final IconThemeData? iconTheme;
final IconThemeData? actionsIconTheme;
final TextTheme? textTheme;
final bool primary;
final bool? centerTitle;
final bool excludeHeaderSemantics;
final double? titleSpacing;
final double? expandedHeight;
final double collapsedHeight;
final double topPadding;
final bool floating;
final bool pinned;
final ShapeBorder? shape;
final double? toolbarHeight;
final double? leadingWidth;
final bool? backwardsCompatibility;
final TextStyle? toolbarTextStyle;
final TextStyle? titleTextStyle;
final SystemUiOverlayStyle? systemOverlayStyle;
final double _bottomHeight;
@override
double get minExtent => collapsedHeight;
@override
double get maxExtent => math.max(
topPadding +
(expandedHeight ?? (toolbarHeight ?? kToolbarHeight) + _bottomHeight),
minExtent);
@override
final TickerProvider vsync;
@override
final FloatingHeaderSnapConfiguration? snapConfiguration;
@override
final OverScrollHeaderStretchConfiguration? stretchConfiguration;
@override
final PersistentHeaderShowOnScreenConfiguration? showOnScreenConfiguration;
@override
Widget build(
BuildContext context, double shrinkOffset, bool overlapsContent) {
final double visibleMainHeight = maxExtent - shrinkOffset - topPadding;
final double extraToolbarHeight = math.max(
minExtent -
_bottomHeight -
topPadding -
(toolbarHeight ?? kToolbarHeight),
0.0);
final double visibleToolbarHeight =
visibleMainHeight - _bottomHeight - extraToolbarHeight;
final bool isPinnedWithOpacityFade =
pinned && floating && bottom != null && extraToolbarHeight == 0.0;
final double toolbarOpacity = !pinned || isPinnedWithOpacityFade
? (visibleToolbarHeight / (toolbarHeight ?? kToolbarHeight))
.clamp(0.0, 1.0)
: 1.0;
appBarStateChangeController?.setValue((math.max(minExtent, maxExtent - shrinkOffset) == minExtent));
final Widget appBar = FlexibleSpaceBar.createSettings(
minExtent: minExtent,
maxExtent: maxExtent,
currentExtent: math.max(minExtent, maxExtent - shrinkOffset),
toolbarOpacity: toolbarOpacity,
child: AppBar(
leading: leading,
automaticallyImplyLeading: automaticallyImplyLeading,
title: title,
actions: actions,
flexibleSpace:
(title == null && flexibleSpace != null && !excludeHeaderSemantics)
? Semantics(child: flexibleSpace, header: true)
: flexibleSpace,
bottom: bottom,
elevation: forceElevated ||
overlapsContent ||
(pinned && shrinkOffset > maxExtent - minExtent)
? elevation
: 0.0,
shadowColor: shadowColor,
backgroundColor: backgroundColor,
foregroundColor: foregroundColor,
brightness: brightness,
iconTheme: iconTheme,
actionsIconTheme: actionsIconTheme,
textTheme: textTheme,
primary: primary,
centerTitle: centerTitle,
excludeHeaderSemantics: excludeHeaderSemantics,
titleSpacing: titleSpacing,
shape: shape,
toolbarOpacity: toolbarOpacity,
bottomOpacity: pinned
? 1.0
: ((visibleMainHeight / _bottomHeight).clamp(0.0, 1.0)),
toolbarHeight: toolbarHeight,
leadingWidth: leadingWidth,
backwardsCompatibility: backwardsCompatibility,
toolbarTextStyle: toolbarTextStyle,
titleTextStyle: titleTextStyle,
systemOverlayStyle: systemOverlayStyle,
),
);
return floating ? _FloatingAppBar(child: appBar) : appBar;
}
@override
bool shouldRebuild(covariant _SliverAppBarDelegate oldDelegate) {
return leading != oldDelegate.leading ||
automaticallyImplyLeading != oldDelegate.automaticallyImplyLeading ||
title != oldDelegate.title ||
actions != oldDelegate.actions ||
flexibleSpace != oldDelegate.flexibleSpace ||
bottom != oldDelegate.bottom ||
_bottomHeight != oldDelegate._bottomHeight ||
elevation != oldDelegate.elevation ||
shadowColor != oldDelegate.shadowColor ||
backgroundColor != oldDelegate.backgroundColor ||
foregroundColor != oldDelegate.foregroundColor ||
brightness != oldDelegate.brightness ||
iconTheme != oldDelegate.iconTheme ||
actionsIconTheme != oldDelegate.actionsIconTheme ||
textTheme != oldDelegate.textTheme ||
primary != oldDelegate.primary ||
centerTitle != oldDelegate.centerTitle ||
titleSpacing != oldDelegate.titleSpacing ||
expandedHeight != oldDelegate.expandedHeight ||
topPadding != oldDelegate.topPadding ||
pinned != oldDelegate.pinned ||
floating != oldDelegate.floating ||
vsync != oldDelegate.vsync ||
snapConfiguration != oldDelegate.snapConfiguration ||
stretchConfiguration != oldDelegate.stretchConfiguration ||
showOnScreenConfiguration != oldDelegate.showOnScreenConfiguration ||
forceElevated != oldDelegate.forceElevated ||
toolbarHeight != oldDelegate.toolbarHeight ||
leadingWidth != oldDelegate.leadingWidth ||
backwardsCompatibility != oldDelegate.backwardsCompatibility ||
toolbarTextStyle != oldDelegate.toolbarTextStyle ||
titleTextStyle != oldDelegate.titleTextStyle ||
systemOverlayStyle != oldDelegate.systemOverlayStyle;
}
@override
String toString() {
return '${describeIdentity(this)}(topPadding: ${topPadding.toStringAsFixed(1)}, bottomHeight: ${_bottomHeight.toStringAsFixed(1)}, ...)';
}
}
class _FloatingAppBar extends StatefulWidget {
const _FloatingAppBar({Key? key, required this.child}) : super(key: key);
final Widget child;
@override
_FloatingAppBarState createState() => _FloatingAppBarState();
}
// A wrapper for the widget created by _SliverAppBarDelegate that starts and
// stops the floating app bar's snap-into-view or snap-out-of-view animation.
class _FloatingAppBarState extends State<_FloatingAppBar> {
ScrollPosition? _position;
@override
void didChangeDependencies() {
super.didChangeDependencies();
if (_position != null)
_position!.isScrollingNotifier.removeListener(_isScrollingListener);
_position = Scrollable.of(context)?.position;
if (_position != null)
_position!.isScrollingNotifier.addListener(_isScrollingListener);
}
@override
void dispose() {
if (_position != null)
_position!.isScrollingNotifier.removeListener(_isScrollingListener);
super.dispose();
}
RenderSliverFloatingPersistentHeader? _headerRenderer() {
return context
.findAncestorRenderObjectOfType<RenderSliverFloatingPersistentHeader>();
}
void _isScrollingListener() {
if (_position == null) return;
// When a scroll stops, then maybe snap the appbar into view.
// Similarly, when a scroll starts, then maybe stop the snap animation.
final RenderSliverFloatingPersistentHeader? header = _headerRenderer();
if (_position!.isScrollingNotifier.value)
header?.maybeStopSnapAnimation(_position!.userScrollDirection);
else
header?.maybeStartSnapAnimation(_position!.userScrollDirection);
}
@override
Widget build(BuildContext context) => widget.child;
}
class AppBarStateChangeController extends ChangeNotifier {
bool _verticalOffsetZero = false;
setValue(bool verticalOffset) {
this._verticalOffsetZero = verticalOffset;
notifyListeners();
}
bool get verticalOffsetZero => _verticalOffsetZero;
}
Copy the code